It's a very common male fantasy to not only be able to watch 2 beautiful women together but also be able to participate. In the competitive BDSM dating arena where there are more submissives than dominants, I suspect these girls are just agreeable to doing whatever they think gives them an edge and are not actually bisexual. I, myself, enjoy a little naughty flirting among friends now and then, but I don't consider myself bi or even bi-curious. Curious about what?! I've experimented. I'm completely hetero. I would never dream of running away from Daddy to be with a woman or suggest that he bring another woman into the relationship, but if he ever wants me to perform with one, I won't refuse.