How can one deal with the wife's mother who practices sorcery and enters the bedroom without permission, and is it permissible to boycott her without depriving the husband of his mother?

The basic principle is to assume the best of Muslims, unless proven otherwise. If what is attributed to the wife's mother is proven, then she must be advised gently. If she does not repent, then you have the right to request a separate dwelling from his mother, and this is your right. As for the wife's mother entering the private room without permission, it is forbidden, and you have the right to prevent her.