I'm sure they would probably be happy enough (if it's three girls anyway) but would they be able to go out for exercise in the winter too? Or be in the hutch?
Obviously the bigger the better, but if you already have the hutch then I think I would just use it and see how they get on in it. All guinea pigs are different and people can't really say "it has to be exactly this size", so see how you feel about it when they're in there.
If it's three girls and they all get on really well, then I would make as much room as possibly for them to run around by making sure there aren't too many accessories or hidey houses, just lots of space.