I wouldn't mind if the girls wanted to fool around with each other. I always view these types of relationships not as the girls all sharing MC, but everyone in the group being "together".
It'll be interesting what happens with the bedroom situation though. Sandra has practically moved into MC's room, Lucy is heading that way. Rebecca sleeps on the couch, will she move into MC's bed too? What about Alice? She was alone crying so she probably needs a cuddle buddy too. I also wonder how comfortable will the girls get with each other, not in sexual ways but in more "casual" ways. Sandra didn't want Aunt to see her naked for example, but if they are all together it would make sense for them to be comfortable around each other in those ways.