>>but I have always been taught that the, "family before oneself" rule.

Well even that is a "relative" rule, not an absolute. For example it wouldn't hold true that if you had an accident and fractured your leg, and your family needed transportation to get haircuts... it wouldn't be expected that you ignore your broken leg and drove them to the barber simply because "family" comes before "oneself"

So it boils down to the relative importance of attending the family dinner vs your needs for health. Now I'm sure that they all underestimate the "importance" of keeping yourself emotionally healthy, and they probably overestimate the importance of dinner (I mean, will the world fall off its axis if you don't go to Thanksgiving dinner? Maybe they think it will!)

So maybe "Family before oneself" means being there when they really need you, when there is something that you can really do to help a need. Maybe it doesn't have to include a dinner that is only "important" because they define it to be so.

So you have to make that evaluation for yourself... you've been given some other options here as well that will help so remember that you have options and don't let them force you!