Don't feel bad, 1undone. You have to do what feels right for you know. Your family will understand in time. It sucks that they are guilt tripping you though. Can they not go without you? I've gone places without my husband because he didn't want to go (because of his anxiety which is now being treated) and I understood why he couldn't go.
To the TC, I'm also going to see a lot of family this week and it's the first time to see them since I stopped drinking. Everyone (except one aunt and my grandma) drinks in my family, so I was worried that it would be awkward. No one has alcoholic tendencies though (not on this side of the family, that comes from my maternal side, thanks Mom!) They are those amazing people that can have two beers over the course of the night and never embarrass themselves, which is what I cannot seem to do. I don't plan to tell anyone the truth because it's just too hard right now, so I told my aunt (who emailed to ask what kind of wine to buy for us) that I had stopped drinking because of headaches.
Well, I do have one cousin fresh out of college who is quite clearly a binge drinker... I hope to maybe have a few quiet words with her and disclose my situation in the hopes it might help her. I don't have ideas that I will cure her instantly, but she's always looked up to me a bit and maybe if she realizes that I'm not perfect she can realize it's okay to admit she's got a problem too.
So yeah, say what feels comfortable and right for you. "No thanks" should be enough, but I know what you mean about being pressured and having to give a stronger answer.