Hm, for the MC, I'm not sure about Yuri, she is into girls, Kristina is a slow process, Ashley is possible, Ammy is a slow process as well, Vivian maybe...
For Kristina, she is virgin, so maybe MC if he seduces her more, maybe the roommate, though somehow i feel the roommate going be the guy they seek, but that is just a geuss, if Kristina turns to females then probably Ashley or Yuri could be, but I think somehow Kristina going be more the female dominator that doesn't give her v-card so easy to anyone. Lucas never going get her v-card willingly so it going be rape or never happen at all.
But these are all just assumption I have, don't know if i'm even gonna be right with some of them, it can always change.