I haven't been to WDW on Xmas eve or day, so maybe my opinion doesn't matter.
We did a group of 11 when I had my inlaws, my parents and my sibs with my family a few years ago.
You will find that if you made the ADR for that large number, you most likely will be limited to the first and last seatings of the day.
We ate at 2 restaurants as a group.
'Ohana (before the menu change) everyone loved it, we had great service, though we had to share 2 tables. If I hadn't asked for a castle view, we might have had one of the bigger tables in the middle. But it was fine.
Liberty Tree Tavern for
MVMCP was the more fun of the 2, I think. My parents and sibs really got into playing with the characters. The food was fantastic, the server great.
I especially liked the family style meal because we all could be together and talk. There was no getting up and going to a buffet which would have cut down on that.
Also, I think Liberty Tree was more traditionally decorated for Christmas and many of the people in my party really enjoyed that. Not that the Polynesian wasn't...I love the Polynesian at Christmas personally.
Good luck deciding.