Hi Mary,
Christmas is a great time to be at Magic Kingdom! It's VERY crowded, but if you're organized with your dining reservations and you go in knowing that you're not going to see EVERY attraction, it's a magical time filled with the sights and sounds of the holidays.
The boat ride from Magic Kingdom to Fort Wilderness Campground takes about 15 minutes. Normally, I would add 15 minutes onto that to account for the time you may have to stand in line waiting for transportation. However, since Christmas week is so busy, you may want to add 30 minutes to that time - especially since you'll be traveling with such a large party.
There's a great for figuring out how long it takes to navigate your way around Walt Disney World at
www.ourlaughingplace.com. Once you're at the site, pull down the
OLP Tools menu on the left hand side of the screen. Select
OLP WDW Transportation Wiz. You'll be able to enter your starting and ending destinations, and your travel time will be calculated for you.
Hope this helps. Have a magical holiday vacation!