I love TE , 1900 PF and R&C but the spaces are going to be tight for such a large group and these are restaurants that are popular.
I want to suggest some restaurants that are larger in space and can more easily accommodate a large group.
WCC, GF Café, Citricos, the Wave, Boma, Trattoria al Forma, Maya Grill, Boatwrights, Turf Club, Yachtsmans St and Morimoto.
In the parK: Biergarten, Marrakesh, Nine Dragons, Via Napoli, Tutto Italia, Tusker House, Brown Derby, H&V can accommodate you but the food is terrible.
Dinner Shows - Hoop De Doo and Luau
It is going to be tough to get ADRs for 21. I would contact WDW's Group Gatherings and ask for their assistance. They specialize in large family planning.