Braintree Area... Family Reunion Restaurant
Is Jimbo's still there? It used to be a decent, reasonably priced seafood restaurant, just down the street from the Sheraton Tara. You could also consider Bertucci's--there's one on Rte. 37 about a mile from the Sheraton.
At the South Shore Plaza, which is across the street there's a new Cheesecake Factory (which I personally can't stand, but many like) and a Legal Sea Food. I don't know if either has a private room.
One exit up Rte 128 there's a popular Italian restaraunt called La Scala, where my in-laws recently had a party for 30 people--I believe they have a private room, though be warned that they only take cash.
Jimbo's is still there and still smells of stale beer. I can't get past the front door. I think it's because they store their empties at the end of the bar, but it's really noticeable and the place is quite run down. I'm a fan of Bertucci's and they could accomodate a group of 50. Also, the Braintree location is quite pleasant. Another option might be Bella's in Rockland. The Braintree Legals, I don't find to be consistent, but they do have separate dining rooms, the staff is very accomodating, and it can be quite good.