A couple of other ideas for you:
1. Get walkie-talkies. Your family may split up at different times, and walkie-talkies will make it that much easier to regroup.
2. Review park maps. If the 15 year old wants to go on Dinosaur, for example, you or your spouse could wait with the other kids at The Boneyard, which they will probably love (and which has only one entrance and exit area). There are many places within WDW where one portion of your family can experience one attraction while the other is on another one, very nearby.
3. Get The 2005 Unofficial Guide to WDW by Bob Sehlinger. I've read many of the competing guidebooks, and this is, hands down, the best. It will answer many other questions you may have.
4. Find attractions entertaining for all ages (the book mentioned above will help with this). I'll throw out a couple:
MK - Buzz Lightyear's Space Ranger Spin, Tomorrowland Transit Authority, Mickey's Philharmagic
Epcot - Living Seas, Innoventions, Spaceship Earth
Disney-MGM - Muppetvision 3D, Who Wants to be a Millionaire - Play It!
AK - Kilimanjaro Safaris, Festival of the Lion King, Flights of Wonder.
I'm sure there are others, but those are the first that come to mind. Some attractions will be too scary for the younger set, some too dull for the older kids.
Have fun! :wave: