If I were in your shoes, I wold plan for the earlier three days as opposed to the latter three. The closer you get to Christmas, the more crowded the parks get. According to Touring Plans, all of the days around Christmas are 10/10 (highest possible attendance). Last year the crowds were not that bad in the early part of our trip, but by about the 22nd, got really bad. So long as you have a plan on what you want to see, you shouldn't have too much trouble.
As for your older "well traveled teens," I would suggest HS and Animal Kingdom from a "ride" standpoint, followed by Magic Kingdom and Epcot. These are merely MY opinions, as I cannot speak for anyone else.