Family Issues Support Group
Family issues is a huge range that go from minor conflict to major misbehaviour and even abuse on the part of individual members of the family occur. Whether you feel you are in a dysfunctional family or you're dealing with a very specific issue, this is the place to talk about it and find others who might be going through the same thing.

If you go onto youtube and watch old Dr. Phil episodes, it usually comes out that the husband is somehow playing into it. Does he go back and forth???
And WTF to have your inlaws let the babymamma live with them? Isn't that a betrayal of their brother? And WHY do brother and sister live with her and another SO? Eeew.
I'd sit down with DH and discuss boundaries.
Maybe join the codependency board???
I can relate, I have a similar problem with my partner's family. He has an ex-girlfriend that was physically, psychologically, and emotionally abusive to him and there is even a police report on her. He told his family repeatedly to stop talking to her and they won't. He told them to stop giving out information about us and they won't. In fact, they freely give out information on us and it's an actual and real threat to our physical safety.
Since they won't change, I've changed my tune. I no longer give them information freely about myself in order to prevent that information from being passed to her or whoever is actually threatening our safety. It really sucks because I actually thought highly of them before but I find this to be crossing my boundaries. It really sucks but it is how it is. We can only change ourselves. I am so sorry you are going through this.