I don't mean this to sound as bad as it does, but why in the world would you want to be around these people? They sound horrible and not a very good environment for a one year olds birthday party.
I really think I'd find a way to bow out gracefully. How long have you been sober? This sounds like a dangerous idea. You can't use alcohol to fall back on when you start feeling uncomfortable. Please, don't go.
Do something better for yourself.