Eliasson,
All power to you to want to keep sober, with all that is going on in your life.
Thinking about your dilemma, I couldn't think of anything worse if I wanted to stay sober this early on in your sobriety. Stuck in a cabin with 3 heavy drinkers. In my drinking days I would have loved it.
Is everyone involved in the trip aware that you are trying to stay sober?
Goodluck if you do decide to go, arm yourself with books, DVDs anything to reinforce your descision to stay sober. If the situation gets tough, go for a walk listen to your mp3, if you have one. download AA speakers, meetings anything that will distract you from joining the drinking.
Enjoy the break. Post often for support
My best wishes
CaiHong