Haven't had it there yet but its where we're having it! We're talking to them when we go for our PS on the 15th of this month. So I can let you know then
I know a lot of brides go to Ohana's. A lot of them do have large to very large groups (I've heard as many as 50). I haven't heard of anyone having it at Narcoosee's before. I don't know how well they handle large groups.
I think I have heard they can put a group in the bar area. I have eaten there when they had a party of about 14-16 in the main area (at one table) they probably can do 25 at a couple of tables. There are catering menus on www.mouseweddings.com If I remember correctly they were $65/$85pp, maybe you could do the regular menu too?