Jenna- another suggestion-
Maybe book afternoon tea at the GF for all the girls and rent a boat for all the men to go fishing, or just cruising around Bay Lake?
I always suggest too, discuss the trip with everyone together, if possible, about a week before you go, and let each person pick one activity that is important to them - whether it's a special photo op in a certain location or with a certain character, dining at a special restaurant, doing an activity outside the parks.
Maybe one adult hanging back with the kids at the resort while the others head to Downtown Disney for the evening.
Get away from the crowd for the night shows, so that you aren't fighting your way through with a big group that might get lost, or
ECV's that will crash in to or clip other guest's feet on the way out. Maybe go to Poly and watch wishes from the Beach. You can see Illuminations pretty well at CBR and BC, and Boardwalk. You won't get the full effect, but it is pretty cool.
Fantasmic- the second show usually is not as crowded. And after the show, sit there for about 15 minutes before heading out, then you are not with the cattle herd. Or, sit at the very top and leave just before the finale.
Don't try to do everything! Pick one attraction in each land/section of each park, and only commit to doing that.
If you want to souvenir shop - go to DTD on a weekday at 9am! There is no one there. We do that all the time. If going in a shop at the parks is a must, also do that first thing, or during lunch time.
And, check the bottom of your receipts for any restaurants you eat at. The last two times we went, we got a coupon at the bottom where if you took your receipt and went to the major gift shop in each park before noon you got 25% off the ENTIRE purchase! And yes, it included Dooney n Bourke! There were no restrictions! It just had to be used before noon, and it expired I think 3 days later.
Send all the men to WWOS to tour and have lunch at the ESPN club there, or go to ESPN club on the Boardwalk while all the ladies and kids do something at DHS or Epcot. Or have the kids do the Pirate Adventure while the moms all go to tea at GF, or a spa treatment?
I think that if you sit down and discuss all these possibilities with everyone together, they might be more open to splitting up for a little bit, maybe at least for one or two days? It will definitely save your sanity, and hopefully prevent some meltdowns.