Is it permissible to boycott one's sister, her husband, and her children because they spread lies and tarnish the reputation of the family's women, especially after the husband attempted to assault the elderly mother and due to the children's bad behavior? If it is not permissible, then what is the solution?

What a man does by slandering chaste women is a grave sin, and whoever assists him is a partner in the sin. His belief in magic, if it pertains to its existence and effect, is correct. However, practicing it or resorting to sorcerers is another grave sin, and magic can be an act of disbelief (kufr) or a grave sin. As for committing acts of polytheism (shirk), its ruling depends on the type of shirk; some of it is clear disbelief, and some is a grave sin, and one might be excused for it due to ignorance. It is obligatory to advise the sister, her husband, and her children gently. If they do not respond, it is permissible to abandon them. If the magic and shirk reach the level of disbelief and the perpetrator persists, the marriage contract between him and his wife is annulled.