I think your daughter would benefit from some counselling. This man hurt your daughter, he isn't safe. Not for her, and not for the little one. He's been violent with her, he's been spiteful to that little boy, going so far as to wish him dead. Why does she want them to build a relationship? She should be actively trying to keep him as far away from her son as possible. Not supervised access, no access ever. Counselling could help her see why she got in a relationship with him in the first place, why she stayed, and most importantly, why she needs to sever all ties now. As for his extended family, it's a shame but as long as they side with him, whether out of fear or genuine belief in his lies, they are also not safe to be around little one. She can't contact them anyways due to court order, so for now they are collateral damage. Maybe in the future they'll change their minds, maybe not. It's not your daughter's concern either way. Her priority has to be her and her son's safety and well being. The rest doesn't matter.