I gold that Benedict XV was an antipope, yes. Because he subtly taught heretical doctrine in his first encyclical, even if he missed it with orthodox statements. If anybody followed him, they were following an antipope.
And if they were not certain, all they had to do was observe his actions in silencing the pious defenders of Tradition and dogma, the
Sodaltium Pianum, who were the greatest public enemies of heresy and Modernism of the time.
His 'Code of Canon Law' was riddled with evil heresies.
Finally, his encyclicals have a distinct Freemasonic flavour, not to mention his telling ties with Gasparri, Rampolla, Bugnini, etc.
I firmly believe that he was not a Vicar of Jesus Christ, but a wolf, who had ZERO authority within the Church.
I also uphold the necessity of the Catholic discipline of abjuration, that it, that a convert to the Faith from heresy or schism is bound by justice to specifically and publicly repudiate under oath all the heresies and sects they may have been subject to prior to their conversion.
Not only did Pius XI not abjure, he never even indicated once that he thought something was wrong with Benedict XV. He publicly accepted him and was subject to him, despite the telltale signs of his invalidity.
Pius XII was even worse, with Modernism and Freemasonic inculcation oozing out of his 'encyclicals'.
In paragraph 87 of Mystici Corporis Christi, he starts under the pretense of condemning an error.
They would attribute the whole spiritual life of Christians and their progress in virtue exclusively to the action of the Divine Spirit, setting aside and neglecting the collaboration which is due from us.
Only to assert another. The following is heresy.
The social Body of Jesus Christ in which each individual member retains his own personal freedom, responsibility, and principles of conduct.
He contradicted Trent (and common sense).
If anyone says that those baptized are by baptism made debtors only to faith alone, but not to the observance of the whole law of Christ, let him be anathema.
If anyone says that those baptized are free from all the precepts of holy Church, whether written or unwritten, so that they are not bound to observe them unless they should wish to submit to them of their own accord, let him be anathema.
So NO, a person does not retain his individual freedom and principles of conduct. What absurdity!
He was a public heretic on this point alone, in addition to later (in his allocution to Italian midwives of Oct. 1951) explicitly stating that the effects of baptism could be supplied even if baptism was lacking. Note that he was the FIRST so-called 'pope' to actually explicitly say this ever since the promulgations of the decrees of Vienne, Florence and Trent.
In the same allocution, he goes on to state that for "grave reasons" (including economic and EUGENIC so-called "indications"!) a person may engage in the rhythm method of BIRTH CONTROL!
Not to mention that he never abjured from his subjection to antipopes Benedict XV and Pius XI.
Pius XII had ZERO authority in the CATHOLIC Church to condemn or to bind anybody.