Hello Stephanie,
Coming from a family of six children I can truly appreciate the logistics of putting together a family vacation. Congratulations on getting everyone to agree to spend their vacation at the Walt Disney World Resort!
Knowing that everyone has separate interests and wants to spend their time at different Theme Parks, a two-day ticket with the Park Hopper Option will be your best value. For example, the kids can spend time at the Magic Kingdom Park and the adults can play at Epcot. For the animal lovers in your group, Disney's Animal Kingdom may be their favorite. The Park Hopper option gives everyone the flexibility to spend the day their way.
Spending family time together is also important and you may agree to meet-up for a parade or fireworks viewing. With the park hopper option, your entire party will be able to travel between Theme Parks for these types of activities.
If you're like my family, food is a great time to get everyone together. One of the best places I have found that accommodates large groups is Via Napoli Ristorante e Pizzeria in Epcot. Their large tables allow everyone to sit together. Just order up several large pizzas and enjoy!
If I could offer another suggestion; have a family photo taken. While you can have photos taken throughout the Theme Parks, Disney Event Photography (disneyfineartphotography.com) is a more formal option. On our last trip my family dressed in coordinating clothing (denim and white) and we had some fabulous photos taken at Disney's Beach Club Resort. It's a great memento of your time together!
Stephanie, wishing you a magical vacation and fond family memories that will last a lifetime!
Leanne T