QUESTION TO OP: So what are your shooting plans? What do you want to shoot? Are you doing video too? Are you just looking to get a few nice group or candid shots of the family on the slopes or are you wanting to go all out nuts and take lots of action shots, "ski-bys" and panning, silhouettes, close ups, etc?
If you are planning on the 'going nuts' plan doing lots of shooting, backpack with equipment, etc then I would take a lightweight tripod & pack stool or something to sit on if you are waiting for long periods for the family to come back around from the last pass, etc. Walkie Talkies might be a good idea too for that so you know when they are coming and won't miss the shots and so you can meet up at designated times or whatever to help you get good shots and still let everyone have fun. Plan out the day's shooting like a pro and decide what, when, where, etc using the slope map and try to get others on board with the plan before you go out.
And if you are 'going nuts', I would just go nuts for one day, get all your shooting in and done and then just ski the rest of the time and give yourself and everyone else a break. Maybe have a Canon D20 rugged cam or inexpensive Rebel with you all the rest of the time.
The part I hate the most about travelling and photography isn't the shooting or even carrying the camera, it's packing/managing all the photo gear, batteries, chargers, other misc stuff you need other than just the camera and lenses. Don't forget to take a power strip (or 2) so you can charge all your batteries, cell phones, PSP/gameboy, iPad things with the rest of the family using the likely one power outlet in the room.