Alright, time for some context...
I have a wonderful relationship with MIL and step-FIL. They treat me like a daughter. FIL and step-MIL? Not so much. Not for a lack of trying, but we don't see eye to eye. I always act friendly and civil the rare times we do see them.
Barring the fact that FH is not very close to FIL either, since we got engaged they're made all sorts of comments, mostly to complain about how we're doing things. They have no say in the wedding and aren't giving us any money, so their comments are meaningless.
A few months ago they decided to get married (after being together 15 years) and FH was the best man. I couldn't go to their wedding because I was already going to my friend of 13 year's wedding to another close friend of mine. FIL understood the situation, step MIL was deeply insulted and told FH that my priorities were all wrong. She hasn't spoken to me since, but every so often she makes quips about me to other people (sister in law mostly).
continued...