When I first met DH he didn't speak to his family, they fell out over something unimportant with his ex. When we got together I spent a lot of time convincing him that it was important to build bridges as we wanted our own family and I wanted them involved.
Long story short, all bridges were built and his family were back in his life, we had a LG and they have been great with her.
We visited regularly and family evening meals always involved wine and nearly always resulted in a heated discussion about one thing or another (they are a family of volatile hot heads) but dont usually involve my husband or I so until the latest visit...
Cutting a longer story even shorter... last visit resulted in MIL massively insulting me (apparently CS is not giving birth properly) and husband falling out with FIL over an old affair his dad had and MIL calling hubs a hypocrite because we met when he was still married (was separated!)
Lots of name calling and shouting between everyone ensued and we were told in no uncertain terms that we were no longer welcome in their house. We left early the next morning.
OH is deeply upset and doesn't seem to care if they are out of our lives for good. I will support hubs and what they did and said was totally out of order but I also feel our LG misses out if she is denied access to her grandparents.