You'll have a great time! If you'll be at the parks for five days, I would recommend going to one park each day, then going back to your favorite on the last day. You might also want to take advantage of the early entrances, although the time you're there shouldn't be too crowded at all.
I would also think about having each person in your group prioritize their favorites (once you're there and the surprise is out, of course!), then you could even do some splitting up in the various parks to make sure everyone sees the things they want to. When I went in a big group (there were 10 of us, including 4 kids), I was nervous that it would be hard to try to agree on everything, but it worked out great. We just agreed to go with the flow, and if the little ones got tired, someone could either go back to the hotel with them or take them on a monorail / train ride or something else quiet.
Be sure to ask a cast member about the stroller switch pass for rides that everyone except the 2YO wants to ride on. It will be a time saver.
Since you have a fairly large group, I would get meal reservations ASAP for whatever you want -- character dining, fantasmic, etc...-- then part of your day will be planned for you.
Have a FABULOUS time!
