I would turn this over to a pro! Or someone like my BIL who is a retired engineer, and a stickler for details.
Seriously, trying to accomodate that many people will be quite a task. Instead of asking how much, start asking exactly what everyone wants, then mark the "absolutely must haves" "would be nice to have, but I can compromise" and the "it isn't important to me."
Have everyone make up a list, including the MOST important, absolute deal breaker! For some, it will be price. For others, it will be onsite lodging. And so forth.
Let everyone submit their lists, and pare them down BEFORE you even start looking. THEN, contact a travel agent (Kingdom Konsultants can help you), contact WDW, whatever.
Just as an example, we have some absolutes for our yearly family reunion. We have to have condos with a full kitchen, phones (we once got stuck without one!) dishwasher, washer and dryer, and minimum steps. There has to be onsite or VERY nearby golf, both indoor and outdoor pools, and tennis.
THEN we add things like health club, sightseeing, beach, watercraft rentals, and activities for the non-golfers. For a couple of people, driving to the site has become a deal breaker; they don't want to fly. Lack of activities for non-golfers has become a deal breaker in our family; we've done EVERYTHING at the place we've stayed at for the past 3 years.
You can do the same for WDW. Do people want villas, deluxe, value? Do you HAVE to be in the same hotel, or do you only want a daily gathering at a park, restaurant, etc? There are a lot of questions to be answered before you start looking.
As you can see, this is going to be a thankless job for someone in your family, but it's worth it when you pull it off. :lol: