Our Lord Jesus Christ promised final perseverance and the Last Sacraments to all who made the Nine First Fridays. Many have experienced and known the Truth of those Promises. Our Lady promised all the graces necessary for salvation in our final hour for all who keep the First 5 Saturdays, pray at least 5 decades and separately mediated for at least 15 minutes on the 15 mysteries of the Rosary. These are sure and simple means of sanctification and salvation for us all, and what is more they will increase love and devotion to the Sacred and Immaculate Hearts, to Holy Mass and to the holy Rosary as we try to practice them. What is important is not to stop after 5 or 9, but to persist in the devotion throughout life, teach it to children, and try to save our souls and that of others.

3 sites that explain this Great Double Novena to the Sacred and Immaculate Hearts together below, the Saviour said: "Prepare yourself with true repentance, if possible go to Confession. Receive Holy Communion on both days (First Friday and First Saturday) The intentions of the Novena must be "to console My Heart and, at the same time, the Immaculate Heart of My Mother."

http://lapieta.tripod.com/dnov_ena.html
https://www.english.santisimavirgen.com.ar/dos_grandes_novenas_eng.htm
https://sites.google.com/site/doublegreatnovena/the-33-promises

The 33 Promises of Jesus to those who make the Double Great Novena: 1. All that they demand through the Heart of My Mother, provided that their requests are compatible with the Will of the Father, I will grant them during the Novena. 2. They will experience in every circuмstance the extraordinary assistance of My Mother as well as her blessings. 3. Peace, Harmony and love will reign in their souls and the souls of the members of their families. 4. I will protect their families from scandals, disappointments, injustice. 5. Married couples will remain together, and if one of the spouses left the home, he or she will come back. 6. The members of their families will understand each other and persevere in the faith. 7. Expectant mothers will experience the special protection of My Mother and receive what they demand for themselves and their children. 8. The Poor will receive shelter and food. 9. I will lead them to love prayer and suffering. They will learn to love God and their neighbors. 10. The sinners will be converted without difficulty, even though somebody else makes the Novena for them. 11. The sinners will not fall back into their previous state. They will not only receive forgiveness for their sins, but also a perfect contrition and, through love, they will recover the innocence of their Baptism. 12. Those who make this Novena in the innocence of their Baptism (particularly the the children) will not offend My Heart by a grave fault until the time of their death. 13. The sinners who sincerely repent will not only escape hell but also purgatory. 14. The lukewarm will become fervent believers; they will perservere and reach perfection and saintliness in no time. 15. If parents or other members of a family make this Novena, no member of that family will be condemned to hell. 16. Many young will be called to religious life, including the priesthood. 17. Unbelievers will become believers, and those who wander without direction (Catholics who broke away) will return to the church. 18. Priests and religious will remain faithful to their vocation. The infidel will receive the grace of a sincere contrition and the possibility of returning to one's vocation. 19. Parents and leaders will receive assistance for their spiritual and material needs. 20. The body will be freed from the temptations of the world and from sin. 21. The proud and the arrogant will become humble, the temperate will be burning with love. 22. Fervent souls will experience the sweetness of prayer and sacrifice; they will never be tormented by anxiety or doubt. 23. The dying will depart this world without agony and without the attacks of satan. 24. The dying will experience an immense desire for eternal life. So they will surrender to My Will and depart this life in the arms of My Mother. 25. They will experience the extraordinary protection of My Mother on the day of the Last Judgment. 26. They will receive the grace of sharing and relieving My suffering and that of My Mother. 27. Those who endeavor to be perfect will obtain, as a privilege, the main virtues of My Mother: humility, love and purity. 28. They will be accompanied by peace and certain inner and external joy during all their lives, whether they are sick or healthy. 29. The priests will receive the grace of living in the presence of My Mother without effort. 30. Those who progress with Me in unity will receive the grace of experiencing this unity. They will know what it means; it does not mean that they will live longer, but that I will live within them. That is to say, I will love with their hearts. I will pray with their souls. I will speak with their tongues. I will serve with all their beings.  They will experience that which is good, beautiful, holy, humble, simple, obedient, precious and admirable within them; it is Me. Me, the Almighty, the Infinite, the only Lord, the only Love. 31. The souls of those who make this Novena will be radiant as the white lilies all around the Heart of My Mother in eternity. 32. I, the Divine Lamb of God, united with My Father and the Holy Spirit, will always rejoice at seeing these souls who, through the Immaculate Heart of Mary, will obtain the glory of eternity. 33. The souls of the priests will always progress in the Faith and virtue.

Source: Little Souls Sisters (Order of Little Souls of the Merciful Heart of Jesus) Note: You can buy "The Double Great Novena" booklet at any St. Pauls Store in the Philippines. Convent: Little Souls Road, Mahogany Avenue, 4120 Tagαytay City, PHILIPPINES P.O. Box 333, Ayala Alabang Post Office, Muntinlupa City, Metro Manila, PHILIPPINES TELEPHONE: Tagαytay (046) 860-1619, Manila (02) 809-2409 FAX: (02) 809-5546

The Lord promises those who make it will receive such abundant graces as to experience freedom from committing mortal sin again, and those who make it will see this for themselves. He also promises to call many, especially among the young, to religious vocations.

Please read the second link, translation's a bit rough but you'll get the gist: "HISTORY:  
The Most Holy Virgin favored with abundant locutions and extraordinary visions during several years, to Sister Natalia Magdolna (1901-1992), Hungarian nun, born near Pozsony (in present Slovakia), pertaining to the congregation of the Sisters of the Good Shepherd of St. Mary Magdalene of Kecskemet.  
Her life was full of supernatural graces and had intense communications with God.  She  died in an odour of sanctity, at an advanced age.  
The promises that we next, are selected from several messages that Jesus and Mary communicated to her, and that were published in the book "La Victoriosa Reina del Mundo" ("the Victorious Queen of the World") by Ediciones Xaverianas, S.A. of C.V. – Ave. Juan Palomar y Arias 694 – Prados Providencia - A.P.1/133-44100 Guadalajara, Jal. (MEXICO).  
Fr. Jeno Krasznay, Spiritual Director of Sister Maria Natalia for some time, famous  European theologian and Auxiliary of Bishop Isvan Hasz, declared these mystical experiences as legitimate, as well as the visions and messages, after a long period of investigation and examination. 

It's an extremely powerful Novena. I encourage all to make it and you will know by experience, as St. Therese once said for a 30 day Holy Cloak Novena to St. Joseph, also very powerful; here, we place devotion to Our Lady's Immaculate Heart next to that of Our Lord's Sacred Heart, just like Jesus asked us at Fatima. We honor the Twin Hearts together and do all our works and actions during the 9 months to make reparation to the Holy Hearts of Jesus and Mary together; I think that's what makes this Novena so powerful.

"I understood that Jesus was requesting the same for his Mother as He had asked St. Margaret Mary for himself.  I asked him Jesus:  
- Should we also console your Mother, since she receives so much ingratitude?  
- Jesus answered:  
- Beloved daughter, if somebody hurts me, this person also hurts my Mother. If somebody consoles me, it consoles my Mother, because my Mother and I are one in the love.  
When The Savior said this to me, I understood many things on the unity of the Sacred  Hearts. 
Jesus also said to me that if somebody goes to confession regularly once a month, is not necessary to go to confession before receiving the holy communion, if one has not  committed any mortal sin since the last confession.  Jesus taught this prayer to me for the first Saturdays: 
 "Most Sacred Heart of Jesus,
I offer this holy communion
through the Immaculate Heart of Mary,
to console You for all the sins
committed against You".

Gentle Reminder. First Friday and First Saturday is now here for the Month of May, dedicated to Our Lady and Her Queenship. The practice of dedicating the Month of May entirely to our Lady with special exercises in Her honor is indulgenced. And let us recall to our minds the wonderful Promise of the Sacred Heart for the 9 First Fridays to St. Margaret Mary, "In the excess of the mercy of My Heart, I promise you that My all powerful Love will grant to all those who will receive Communion on the First Fridays, for nine consecutive months, the grace of final perseverance: they will not die in My displeasure, nor without receiving the [last] Sacraments; and My Heart will be their secure refuge in that last hour."

This Month of May, Mary Crowning Month, is the "month which the piety of the faithful has especially dedicated to Our Blessed Lady," and it is the occasion for a "moving tribute of faith and love which Catholics in every part of the world [pay] to the Queen of Heaven. During this month Christians, both in church and in the privacy of the home, offer up to Mary from their hearts an especially fervent and loving homage of prayer and veneration. In this month, too, the benefits of God's mercy come down to us from her throne in greater abundance" (Paul VI: Encyclical on the Month of May, no. 1) ... The practice [of specially consecrating the Month of May to devotion toward the Mother of God] was granted a partial indulgence by Pius VII in 1815 and a plenary indulgence by Pius IX in 1859." Excerpted from Enchiridion of Indulgences.

Prayer of the Month:

An Act of Consecration to the Blessed Virgin Mary

Holy Mary, Mother of God and Virgin, I choose Thee this [month] as my Queen, Patron, and Advocate, and firmly resolve and purpose never to abandon Thee, never to say or do anything against Thee, nor to permit that aught be done by others to dishonor Thee. Receive me, then, I conjure thee, as Thy perpetual servant; assist me in all my actions, and do not abandon me at the hour of my death. Amen. — https://www.catholicculture.org/culture/liturgicalyear/overviews/months/05_1.cfm

We can unite ourselves to and repeat in our own names together with the Pope and the Bishops this partial Papal Consecration, awaiting the Consecration of Russia.

"1. "We have recourse to your protection, holy Mother of God".

O mother of individuals and peoples, you who "know all their sufferings and their hopes", you who have a mother’s awareness of all the struggles between good and evil, between light and darkness, which afflicts the modern world, accept the cry which we, as though moved by the Holy Spirit, address directly to your Heart. Embrace, with the love of the Mother and Handmaid, this human world of ours, which we entrust and consecrate to you, for we are full of disquiet for the earthly and eternal destiny of individuals and peoples.

In a special way we entrust and consecrate to you those individuals and nations which particularly need to be entrusted and consecrated.

"We have recourse to your protection, holy Mother of God: reject not the prayers we send up to you in our necessities".

Reject them not!

Accept our humble trust—and our act of entrusting!

2. "For God so loved the world that he gave his only Son, that whoever believes in him should not perish but have eternal life" (Jn 3:16).

It was precisely by reason of this love that the Son of God consecrated himself for all mankind: "And for their sake I consecrate myself, that they also may be consecrated in truth" (Jn 17:19).

By reason of that consecration the disciples of all ages are called to spend themselves for the salvation of the world, and to supplement Christ’s afflictions for the sake of his body, that is the Church (cf. 2 Cor 12:15; Col 1:24).

Before you, Mother of Christ, before your Immaculate Heart, I today, together with the whole Church, unite myself with our Redeemer in this his consecration for the world and for people which only in his divine Heart has the power to obtain pardon and to secure reparation.

The power of this consecration lasts for all time and embraces all individuals, peoples and nations. It overcomes every evil that the spirit of darkness is able to awaken, and has in fact awakened in our times, in the heart of man and in his history.

The Church, the Mystical Body of Christ, unites herself, through the service of Peter’s successor, to this consecration by our Redeemer ..." https://www.catholicculture.org/culture/library/view.cfm?recnum=630