We had a group of 14 - 16 in Nov, Thanksgiving week to be exact. With each PS I was told '2 tables, 3 tables, etc.' but in actuality, we sat together at many of the restaurants.
DINNERS
Brown Derby - one long table
Cinderella's castle - 3 tables, but all along the wall right next to each other
Yachtsman - one long table
Hoop Dee Doo - one long table
Teppanyaki - 2 tables
Le Cellier - one long table
Narcoossee's - one table, but only the adults ate there
BREAKFASTS
Donald's - 2 tables
Cape May - 4 tables
Hollywood & Vine - 3 tables next to each other
Crystal Palace - 3 tables next to each other
1900 Park Fare - 3 tables next to each other
Chef Mickey's - 3 tables next to each other
They always say they can't promise you'll be together, but they do their best to seat you together.
Depending on how long you are going for, you may want to plan at least one dinner where each family goes their own way. We did not stay together all day, but eating pretty much every meal together got to be a little much. Also we did have a larger group, but make sure you allow plenty of time for meals. By the time they take 14 orders, give out 14 drinks, 14 appetizers, etc., etc., hours go by, so watch it if you are dining before Fantasmic, or Illuminations or spectro. Allow yourself plenty of time, and remember, your whole group must be present before they will seat you, and then even then, you often have to wait.