Economizing: share the condo. This makes meals affordable. esp. w/teens--lunch in the lodge for a family of 5 is a killer. We've even shipped food in advance, or checked a box of staples as luggage, when we thought we were going to be limited to on the mtn. groceries. Unless you're someplace with really great restaurants, where the expense is worth it, dining out just becomes costly calories--microwave frozen casserole in the condo may not be exquisite cuisine, but it's easy, nourishing, and CHEAP. By the way, kids love those "just add water" baking mixes for dessert and breakfast muffins. Get within walking or bus distance of slopes (a resort with a transit system like Whistler's makes many locations "convenient") and the condo also becomes a retreat for tired or discouraged beginners, with more to do than hang out in the dayroom. All our past multi-family vacations have seen a constant occupancy of the condo, this one for cocoa, that one for a nap, another quitting early or starting late. Don't go too small, make sure people have private, retreat space. Committing to 2nd hand gear in advance is a good idea if possible, pitch immediate resale value if they abandon the sport, with $ loss still being less than rental fees, plus time savings of not being in the rental que all morning.
Fun: Friends are so important to teens, plus there's the embaressment of being a beginner, so picking a resort that's bigger may actually be better, with "more to do" than just ski (a pool's great), esp. if skiing turns out to be a bust for one of them. An isolated resort like Big Sky probably's the wrong place to start someone, unless you're all keen on "quality family time". Prep them with videos, Warren Miller's old Learn to Ski ones are great, though dated (the principles remain the same) and available cheap at half.com. Take videos and board games. Also encourage some kind of pre-conditioning. If they aren't athletic already, learning to ski can really take a toll. Some beginners become discouraged from fatigue, not lack of skill. Finally, make sure they've got the clothing for the sport. Like fatigue, cold and wet sour as many beginners as falling down and fear.