I have the idea that a threesome where the girl brings her sister would be hot. But the little devil on my shoulder says if you look at the big picture it would be just unethical or incest. I think most of the people don't think of their siblings that way, but what about a threesome situation? If you don't touch them that way, just the 3rd party and you only have fun together? I'm curious if that actually happens in real life or remains a fantasy? Got poll options for everybody and this is a private voting. If you don't have a sister or brother you can choose that option. I think only those can answer really who have siblings. Don't take into account your current relationship status.