What is the ruling on the actions of a divorced sister's ex-husband, such as harassment, attempted molestation, and threatening to take the children, and is it permissible to prevent the ex-husband from entering the house after all these actions?

If the husband desires to have intercourse with his wife after khul‘ (divorce initiated by the wife), it is a reprehensible act and a grave sin, and he must be prevented from it. The father has a prior right to custody if the parents separate, each residing in a different country. This is the view of the majority of scholars. Some scholars, however, hold that the mother has a greater right to custody if the child's interest necessitates it, even if she is in another country. The husband has the right to prevent his wife from leaving his house for study or other non-essential matters, and he has guardianship over her.