I can really relate to all the family drama, southern food, and people being offended if you aren't eating something in a combinatin of my side and my in-laws, which I'm much closer to actually. Either there's food I'm not interested in and they will be offended, or there's food I want, but it's something with tons of calories like a great big bowl of gumbo and rice w/crab legs on new years. omg. yum!
so in addition to bringing some healthy dishes, and just getting what you want as much as possible, try to portion out your food so it's ready to go for when you come back, if you have the freezer/fridge room. Or at least make a plan of your menu and workouts for after.
Also, getting that workout in helps, specifically, doing a workout with an afterburn effect or a workout that makes u sore after. for me, that's plyo. something like sts plyo legs. lots of jumping lunges, squats, jumping/turn squats, speed skaters. If I'm sore during the big meal, it's a reminder to not eat back my calories in pie. it doesn't always work, but it also prevents you from gaining very much.
and after all treat it as just 1 meal. make your other meals healthy, try to bring a healtheir dessert if you can. maybe see if a friend can be your workout buddy later in the week, to make sure you gtet back on track.
Also I can relate to all the drama at holidays. my side of the family is always very dramatic me included. I just thought it was normal for a really long time growing up. I also understand what it's like to not live with your mom, and then live with her again. it wasn't as rosy as I had thought it would be. but I've tried to learn from it. and we are trying to be much less dramatic raising our kids. holidays are for getting along, not telling off your relatives that you haven't seen in ages.
Anyway, good luck with it. remember it's just food. It's only 1 meal. Try to enjoy yourself with your friends or family. maybe get the family involved in a game. my family is a big fan of taboo and video games.