I don't think I have any magical advice that can with the situation, but I can DEFINITELY relate! In 2008, I was 180 pounds. Then, I lost 80 pounds over ~2 years. Maintained for awhile, and then I gained it all back. I haven't seen most of my relatives since I was 100 pounds or so, and currently I'm at around 165... I haven't even seen my dad since I was thin. My parents were so proud of me for losing weight, and my family values thinness (though also health in general) to a great extent.. Nobody else in my family has a weight problem, really. Lucky me
Anyway, I definitely get that it's super stressful, and EMBARRASSING! But of course, you are the one who is going to be 10 times more focused on your weight gain than any of your family members will be. Plus, in my experience, people always underestimate other peoples' weight gain, so a gain of 20 pounds is usually estimated to be maybe a gain of 12 pounds. Especially if you carry your weight somewhat decently.
The best thing I did for myself was go buy a few clothing items that seem flattering, and I will wear my new clothes when I'm visiting my family. I don't know what else you can do... Just take comfort in the fact that weight fluctuation is really common and your family is probably not going to care all that much. They just want to see you! Plus, you're keeping things interesting by looking different each time
Let's just try not to let this ruin our holidays.
You're not alone.