In my experience, I would do my best to avoid subjects that could get heated and I’d be pleasant as I could without being fake. On this subject, you hold all the aces so just be gracious. Reality is just about to bite the idiots on the butt so let that be their chastisement.
Maybe if you’re gracious they’ll give your opinion a little more respect in the future? If not, don’t waste any more effort trying to help them in the future because they’re likely unreachable. Stick to superficial topics when you’re around them. Ultimately these people are pitiable.
Unfortunately their nature is such that they refuse to stick to superficial topics. They exist for the purpose of creating discord. They count on the good graces of civil, peaceful, respectful people in order to spew their falsehoods and delusions unchallenged.
Any pushback is conveniently interpreted as intolerance and an unwillingness to "get along with family". It is an especially successful tactic at holiday gatherings because they know that most are more apt to suck up the BS for one day "with family". IOW, they intentionally survey and then abuse the good manners of others. Typical MO of abusers, bullies, manipulators, pieces of work that love darkness and hate the light.
I'm with the other posters who say f' 'em. No more of their sick games invading our own peaceful homes. Let them dumpster dive at KFC for their Thanksgiving pickins.
Many families are only now coming to the realization that these extented family members never had any intention of getting along. They were just showing up for the free feast, and coming in with a chip on their shoulders at that, looking to create a dust-up.