mom2grace said:
No WDW property is large enough for 15, but you might consider renting DVC points for 2 2 bedrooms at a DVC resort.
I would ask everyone for the 1 thing that they absolutely MUST do, as a starting point for planning. I wouldn't expect everyone to spend every day together, maybe do a few sit down meals together, although I am sure you will have 2 tables at most restaurants.
I absolutely agree with these points.
One change I would do though... if you can, try to rent a 3BR Grand Villa and a 2BR at Old Key West.
4 bedrooms would still be "cozy" for 15, in my opinion. The 5th bedroom should allow the 4 groups of adults each with a bedroom and the 2 18 year olds could be in the 5th BR. The living area of the 2BR could become the sleeping area for the 5, 6, and 9 year olds and the 3 and 4 year olds can bunk in with their parents.
This will leave the marvelous living/kitchen/dining area in the Grand Villa available for family gathering/breakfast socializing/planning space without taking up anyone's sleeping area.
Also, in the GV, there is really enough room for everyone to eat at the villa if you want to do some inexpensive/easy meals and have more family time without bothering other patrons.
I know when we did 2 3BR units in 1998 (17 of us) we did have dinner with everyone in one villa (8 at the main table, 4 at the small table in the living room and the rest either on the balcony table or sitting on the sofa). It was a lot of fun, and was certainly much less expensive than eating out for a couple of dinners.
We did simple things like Stauffer's lasagna, salad and garlic bread or tacos.
The accomodations aren't cheap, but they do provide more together time (if that is what you are looking for) than a bunch of hotel rooms and eating in the villa can reduce out of pocket for food dramatically.
As for activities, I like the idea of asking each person what 1 thing they want to do most. That is a good place to start.
When our family gets together like this, though, the number 1 rule is "it's vacation, no one has to do something they don't want to do".
With that as the attitude, we are always able to come up with at least a few activities that everyone is willing to take part in and therefore we have plenty of "whole family" memories to take away without stressing anyone out because they have to stand in the queue for ANOTHER attraction.