I would say, try to look at the situation objectively, don’t blame one single person as the ‘source’ of all the problems…. and if you are the person who is being blamed - as is so often the case with daughters in law - be prepared to step back entirely.
DH’s family are screwed up. Very immature, demanding, narcissistic mum. Slightly inept, henpecked dad. Kids packed off to boarding school at 7. DH has a younger brother who was always jealous of him. They weren’t encouraged to be close.
Over a decade ago, a big family row kicked off - I won’t bore you with details. Somehow in the fallout of this I ended up being blamed as the reason for all their problems, despite the fact they’d obviously had family issues since long before I met DH!
It was pretty awful for me and for DH. He wanted to retain a relationship with them despite how nasty they were to me. This risked becoming a point of conflict between us, and then I thought, right - I will step back from this entirely. Let them think whatever about me, I don’t care. I don’t have to deal with their nonsense. Let them deal with their own issues.
Guess what? DH now has very minimal contact with parents and doesn’t talk to his brother - and none of this has anything to do with me.