Those of you dealing with in laws who treat you terribly, I'm sorry. That's awful.
I am honestly so impressed with the # of people who had to draw such extreme boundaries with their families of origin in the best interests of their own spouses and children. Choosing not to participate in someone else's crazy can be difficult to implement.
If anybody is dealing with this issue and on the fence about cutting ties, I can't even begin to express how much better life can be when you remove yourself, and especially your family, from toxic relatives. The MIL I mentioned was a pretty horrible human overall, and due to the strict Catholic beliefs, did not believe in divorce. As a result, she made life hell for her husband, who ended up dying in his mid-fifties. I have no issue with reaching the conclusion that he ( a truly wonderful guy) could of led a long, healthy life if he has just gotten the hell away from her, decades earlier. When the MIL announced that she was boycotting our wedding and cutting ties, I was ready to do back flips of joy. When she wanted a relationship with her grandchildren, and made it clear that she was still the same nasty bitch she had always been, the DW and I knew that she had to be removed from scene. The wife still stayed in contact until her mom passed, many years later, but the kids and I were off limits. We never regretted the choice we made.
The other possibility is that you can try a tough love move to snap somebody out of their behavior. My mother was an extremely high functioning alcoholic. As she got older, and her disease progressed, she was essentially living on white wine
and vitamins. While visiting my family, she started making some really nasty comments that, after she left to return home, caused the wife and I to look at each other and say, "I can't fucking BELIEVE she said that!". After three really nasty shots at the wife and I, over a few months, we just gave her the cold shoulder for a while. About six months later, she jumped on the phone and wanted to confront me as to "what my problem is". I coldly relayed the last several off the charts nasty comments to her, and explained that we were no longer tolerating that kind of abuse in our home. She was stunned to hear that this kind of comment was being attributed to her, and apologized. At that point it was obvious that she was no longer "all there" when it came to being an alcoholic, and really had no idea that such cutting nastiness was freely flowing out of her mouth. She decided that having a relationship was worth it to her, and stopped the nastiness.