I sat my partner down last night and we had a conversation about what to do. He's adamant that his dad won't listen to anything we say and definitely won't ignore her if we tell him too. I just told him that his dad HAS to listen and it's his job to lay down the law because FIL definitely won't pay any attention to what I say (sexist pig). And we agreed that if worse comes to worse, we will just have to tell his dad that he can't visit until he does what we say.
Wish us luck! At least I have until Christmas to try and work out how to hide my frustrations and that urge to scream at him