I don't know, I don't think it'd be that bad... think your just letting panic get to your head... the spotlight isn't really on you, so you can be silent and eat your food w/o ppl really noticing... just put on a polite smile and deal with it like any other social horror one must attend (virtually all my family meetings and stuff are like it... I'd rather NOT go, but sometimes you have to).
I don't think you'll make a fool of yourself... wait a while before you say anything if your worried, if ppl are joking in such a manner than fine, join in, but if they seem all stiff and proper, keep the jokes to yourself, because might not be appreciated... honestly, your most likely to end up being "paired" up with his girlfriend, and talking with her for most the night... so who knows, maybe you can make a friend out of it!
I mean, I know I'd rather avoid it... but I've attended friends meetings w/ their families and stuff, and very similar thing... I just sit there quietly, eat my food and speak up if someone asks me something or if I hear something I can contribute to... not the most pleasant set of affairs, but if it makes my friend happy I was there, its worth it...
Really, your just letting fear and anticipation let you panic... but when you get into the moment, it won't be nearly so bad...