Is their a way to revert the girls to different stages because as of current (To my knowledge anyway) it's impossible to do everything in one save file.
You can view older sprites in the stats menu, but I think the only way to actually revert them is for them to lose the weight. It'll happen slowly if their metabolism and self-control haven't been whittled down, but I must emphasize how slowly it goes (since this is a weight gain game after all)