This family has too many friends in high places and your daughter in my opinion has to come before your son, who is not in danger. Can't you explain the whole dynamic to him?
Your SS is not breaking up the family. Your husband and his family is. All of them. They are making sure SS is protected although I think it's matter of time before he perps on somebody who turns him in, maybe not in this town.
in my opinion you should leave the area in this family's control. Please be safe