if I wanted to bring a large family group is it possible to rent rent the whole place for a couple of nights,# of beds,# of rooms?etc
You can rent the whole island depending on how many people are in your group. The 2nd floor keeper's apartment has a queen bedroom and a pull out sofa in the living room. The bunk room has 1 set of bunkbeds. The downstairs bedrooms each sleep two, as does the foghorn room and the barracks. You can also put a cot or two in the barracks room if you are traveling with kids.
Yes. From what we were told, anyone can rent this house, probably up to 6 people. It sounds like you would do some upkeep in exchange for the rent or pay rent, whichever works for your group. Definitely get in touch with them for the specifics. It's such quaint place and the surrounding area is awesome for some hiking and boating.
Get an answer from Rose Island Lighthouse staff and past guests.