If you don't mind, I'd like to offer some general tips on a multi-generational, larger-party trip, as we did one recently. Your group is wise to appoint you the leader, as this will keep everything far simpler!
The Shamelessly OCD Woman's Guide to Planning a Large-Group WDW Trip:
1 - With that many people, the dining plan was a good choice. Call the dining line to get what you need, as they'll have options (like reserving "split tables" when it looks like there's no availability) that the online system can't give you.
2 - Lead an organizational meeting. My background is in law/education, so I am the Queen of Binders and Handouts, which came in very handy. Before the ADRs had to be made, we had everybody over and watched the Disney Vacation Planning video together, as some of our party had never been to WDW, and others hadn't been in years. Then we discussed: (1) daily schedule and generalized itinerary, which included pre-planned mornings with FP+ that everyone would be free to take or leave as they desired -- our motto was, It's okay to depart from the plan or go your own way -- we just need to have a plan in the first place!; nap breaks that everyone could take or leave as they desired; and table-service dinner reservations that we would all commit to attending each day so we could all catch up; (2) dining preferences and desires, including allergies and aversions, so I could make group dinner ADRs at places people would like, and recommend appropriate CS options; (3) how the DDP worked, including daily credits, kids' menu, and what a "snack" symbol looks like, and a discussion of how we were going to split up dining gratuities; (4) an overview of Magical Express, baggage transfer and the Disney transportation system; (5) an overview of attractions, plus taking notes on things like kids' heights, "Aunt so-and-so can't do spinners," or "Uncle so-and-so won't ride coasters or simulators," so I could make FP+ that were appropriate for everyone; (6) an overview of MagicBands and how they work, and taking notes on what color/name each person wanted on their band; (7) because we were flying and some of our party hadn't done it in awhile, copies of our reservation information, airline baggage restrictions, the 3-1-1 rule, how to get through security with a minimum of fuss, as well as airport parking rates and arrangements to carpool to the airport; and (8) distribution of a sample packing list for infrequent travelers, and a discussion of who-is-packing-what (for items we could share, to avoid overpacking). It sounds like a lot, but we did it in 90 minutes and by the time it was over, I was able to make reservations and FP+ without fear that anyone was going to be disappointed.
3 - Just before you leave, create a little folder for each family or hotel room, to help keep the whole group literally "on the same page." Inside, put things like: (1) a rough copy of your proposed itinerary for each day (e.g., which park(s) you suggest visiting that day and which lands you propose to tour, with FP+ and ADR information, as well as times for any fixed-schedule shows or parades you plan to see -- again, always with the understanding that anyone who wants to do something else is free to do so, and can look forward to catching up with the group later; (2) the schedule for park hours and EMH for each day of your trip; (3) park maps; (4) hotel map, with transportation info. on how to get to each park or other planned destination, from your hotel; and (5) important phone numbers (cell numbers for each person in your party, plus your hotel front desk, park "lost and found" numbers, stroller rental, Kids Night Out babysitting, taxi, etc.).
