We all have similar problems.
But remember, once upon a time, it was considered extremely rude for guests to discuss either religion or politics. Remind them gently that you don’t agree on certain things, but you all love each other and everybody’s there just to be together, eat good food, and have a good time.
My own son is a very pro-union absolute jerk who specializes in taunting me, his sisters and a couple of other other conservatives in the family. Since he doesn’t live near us, he does it electronically. But one time, after a particularly bad blow up during one of his visits, I made it clear that we really don’t need to talk about these things, but about the things we have in common (in my case, fishing, music, etc.). He’s been pretty good on his visits since then.
So it’s your house and you can lay down the ground rules pleasantly and politely at the start. They may not abide by the rules, but that’s about all you can do. And if a fight breaks out, it makes them and not you look like the people who ruined Thanksgiving.
Had to do exactly that with my son recently. Fortunately, my daughter is more conservative - and a FReeper, to boot. :-)
keep a taser and pepper spray nearby in case he gets obnoxious