What is the ruling on a sister boycotting her brother if he does not divorce his wife for life?

A man is not obligated to obey his sister, mother, or anyone else in divorcing his wife. There is no sin upon him if he refuses this; rather, the sin is upon her if she severs ties of kinship with him due to his refusal. The man should try to reconcile with her, maintain ties with her, and treat her well, even if she acts poorly, in the hope that she may come to her senses.