I need some advice on how to improve things with my in-laws. If there is an issue with your in-laws, how do you and your SO handle it?

Just some backstory on our situation in case it makes a difference. Sorry it is so long! DH and I are not on speaking terms with my SIL and have not been for about 2 years now. She is very selfish and disrespectful and eventually we had to cut ties for our sanity and to protect our family and marriage. DH's parents live near SIL and rely on her for a lot so they obviously sided with her (without even asking or listening to our side) so things have been tense with them ever since. We still see them but honestly do not put in the effort because they don't either. After a big family party back in early April SIL was back to her old ways and I had had enough so I did what I needed to fix what she had done to us and it royally pissed her off to the extent that she threatened us and now, almost 4 months later has gotten DH's entire extended family involved. DH's parents, aunts, uncles, cousins, etc. are all mad at us for this drama with SIL when she is the one that has been bullying us for years. DH is not the type to involve other people or say mean things. His go-to "solution" is to ignore something and hope it goes away. If we want any type of relationship with his family, that is not going to work. I don't mind confrontation and making my point but it is his family and not my place to do it. DH is really upset but has just kind of given up. I have no idea what to do.