You are so very brave!!! My only suggestion is that you allow alone time for each family....half days, whole days, or maybe even multiple days. Some people are early risers. Some are not. Some people can go, go, go. Others cannot. Some people are willing to try each and every attraction, and others may be more particular. Some people can deal with the stimulation, crowds, and heat better than others. Be aware, and allow time for everybody to do their own thing. Teens may even want to split up for an hour or two within the park and meet the rest of you later at a designated time and place. We did this with our 12 and 15 y.o. during our fall trip. You would have thought that they had been given the keys to the kingdom! They thought they were pretty special to have this alone time, and my husb and I also appreciated our time alone.
I wish you all a wonderful time! I can see all the smiles already, and I'm sure many magical memories will be made. Have fun!
To add to the anticipation and excitement, order the WDW vacation videos for each family.