Thing is, I have WASPy relatives that I'm unfortunately going to be spending thanksgiving with as well and they're capital C CHUDs. I'm warning you, getting all up in their face is what they want. You could call them cracker all you want but CHUDs are mostly immune to emotional damage. If you go about it like that, all they'll do is laugh about it at work about how they totally owned their SJW relatives.
There's a more nuanced strategy I take. Just make them feel like the burden. You're there to have fun and they're the ones that cannot put politics aside for a single goddamn day if you have to call something out make sure to end it with "look, I'm not trying to argue, I'm just saying."