Kona at the Poly has Great food & is reasonably priced given the quality. As I recall, there are lots of free-standing tables that can be moved together.
Also, when we were at Boma for breakfast earlier this month, there was a family reunion type breakfast going on. Our server said that the last headcount on it was 48! They took up an entire section & people were coming & going the whole time we were there. Even tho it was breakfast that we saw, I'm sure they could handle dinner the same way.
We did a dinner at Chef Mickey's for 21 for my sons birthday. I did a couple DIS meets ages ago that were fairly large, dinner at Spoodles for 18 and breakfast at Chef Mickeys for 26. Both were nice & relatively inexpensive. I did have to go thru Group Sales for the Spoodles meet. I'm not a Chef Mickey's fan at all anymore tho. The last couple meals I had there were pretty awful.