Stretch before and after you ski.
Before do some squats and work with medicine bells. Do some leg kicks against a wall.
After, do some cool down things before you sit down for the end of the day.
I disagree with most of the balance training. Standing on a balance board or bosu ball is not the same as skiing. These balance tools are an unstable surface you are standing in a static position on, whereas skiing you are on a solid surface, exerting pressure. There's been a lot of debate about this in the fitness community over the years.
For most of you, strength is what you need to improve, especially the 6'0 140# skinny aliens. Do heavy squats (3-6 reps), deadlifts and presses. For conditioning, hill sprints, C2 rowing, tabata bodyweight stuff (push-ups, sit-ups etc), burpees and do some longer endurance stuff (5km/10km trail runs) once in a while. Hiking with a pack for a day is also good.