I hope your in-laws do not live near you. I have a neice and her family in Scotland. She told her mother and dad(my brother) that they will not take their phone calls anymore (from CA). My brother and his wife are using drugs and into satanic ways. So, my husband and I have been adopted as her parents and grandparents to ou great nieces.
So, she put her foot down and said no more! Block their calls, whatever you have to do, lay down the law!
Drugs are open portals to the demonic if they are used to intentionally "get high." Lots of sad cases because of drugs.

God Bless you for being guardians of those girls.
Ask a Priest about exorcism prayers to be said for your brother and his wife. Father Chad Ripperger is an exorcist, and he gives advice on the authority of parents over kids, etc. Drugs can openly bring about spiritual attacks on the children of their parents that are using drugs.
Find a way to ensure these girls/ladies are protected--wearing a Miraculous Medal, brown scapular, etc. At least a Miraculous medal. You could send them each a nice one and say it is a reminder you are thinking of them always. Whatever will work in you situation.
But those nieces need to be physically and spiritually shielded. Satanism adds a whole other layer to deal with. Aye.
Exorcists are not usually very public for many reasons, but each Priest also has the power to do them (if I understand correctly), if they have been given permission by their Bishop. There are minor exorcisms and major ones. Out of my league to advise you on the major ones. Minor exorcism prayers are available to the laity.
Eg. The short version of the Saint Michael prayer commonly said after Low Mass. The longer version is reserved only for Priests!
I will pray for your situation also. God Bless, Anne