There is a book called; "Toxic Parents: Overcoming Their Hurtful Legacy and Reclaiming Your Life".
I had my (ex)husband read it and it helped him understand so much about his upbringing and his parents behaviors. His parents, like yours, had large extended families ( eleven siblings between them, who coincidentally all got along amongst themselves) and they did not communicate with _any_ of them. Always because the _other_ people had done or said something they disapproved of. It was bizarre and quite honestly pathological.
You are in a tough spot. It does sound like you found a good man, serious about his recovery. I wish you the best of luck.
*hugs*