for a westcoast experience, if it was just yourself i'd say alta, whistler or Jackson Hole, but since it's a family trip with 4 families, don't go to Whistler.
No seriously Whistler can't go wrong in March. Usually, thats when you get some good dumps. The last 3 spring breaks have been awesome, last year I had an 80cm day. The village has tons of shopping, americans, aussies, short skirts, luxurious hotels. So if your rents have the money go to Colorado. Co is the place to be in march