I am so very sorry you are having to deal with this. I am wondering what your wife makes of all this and whether she, from her own experiences, has any insight into why these folks are being so provocative.

In my experience and generally speaking, bringing up politics in any multi-generational family is likely the road to nowhere. And trying to tell this group of people that you don't want to discuss or get into political issues seems like it is likely to fall on deaf ears. You could, of course, try, but I wouldn't hold out great hope for a transformative experience there.

You may just end up being one of those families that spends very little time together. They exist. I am in one. There are worse things. However you elect to proceed, I personally would not put up with this in-your-face gamesmanship (nor would I if they were all MSNBC fanatics). It's just inappropriate. And no fun. Life's short. Spend it with people you like.