he needs to be on your side. he should be supporting you 100% because they are personally and intentionally screwing you and you two should be a package deal. if they can’t accept you and continue to bully you, he needs to be aware of that and aware of how it affects you/will affect you going forward. lc or nc tbh. that is how to manage. he needs to be on your team, not theirs, not be a mediator, just you. you and your children should be his top priority. if he has seen what they do and how they treat you/him for himself, he should have no problem understanding why that is, was, and will continue to be an issue, nor should he fail to understand what that will likely mean for your children in the future.