We've had many awesome opportunities to enjoy meals at Disney with a large family group. Just some experiences we've had (not sure what your family likes!). 1) 'OHana, where we've had as many as 20 of us sitting at the same table - we also have an amazing family photo from the Poly lobby!; 2) Boma, where we also got to sit together - and the buffet allowed people with different tastes to enjoy what they wanted; 3) Chef Mickeys - although not a fancy dining experience, we did sit near each other - and they took a family photo for us as we entered (another photo on our wall at home!); 4) We also did the MK fireworks/dessert party, and that worked out very well, too!
Funny story - if we have a time and place we absolutely want to get the entire family together - at least once, my wife and I offer to treat for that meal. Funny how everyone shows up when someone else is buying!! Good luck with your plans. Sounds like an awesome trip.