What is the way to deal with my sister-in-law's accusation that I used witchcraft on her to disrupt her life, especially after years of me avoiding her due to her malice and scheming, and what is the best course of action for my husband regarding his brother, who believes these fabrications and seeks to ruin our home and sever kinship ties?

Your husband's brother is not permitted to accuse you of performing magic on his wife without evidence, as this is a grave slander and a major sin. You must continue to advise him and remind him of Allah and the ill consequences of his actions. He should also be advised by someone whose words he respects. One who is falsely accused has the right to defend themselves, and we advise exercising wisdom to avoid severing kinship ties. If he strongly suspects his wife has been afflicted by magic, treatment is readily available through ruqyah (Islamic incantation).