After putting more thought into it, I feel like I'd prefer to play the human son of a faculty member. I feel like it would make sense that some of the Humanities (no pun intended) would be taught by human professors, or some at least, in order to teach what are described as sheltered succubi and incubi about humanity from first-hand experience.
However, I also understand wanting to avoid the possibility that you have 12 players as humans and 3 succubi, thus negating the purpose of the game.
As long as we have enough Succubi students and faculty, I'm not opposed to having a human being part of the staff, though he would have to limit his presence around students or wear a ward to protect himself. Think of Succubi as hungry vampires with short self-control, but instead of drinking blood, they want to have sex which isn't so bad if its one on one with a student, but with multiple students, it can become dangerous unless a teacher is nearby to intervene.
With these Succubi, they can be impregnated by a human, but the child will still be born either a Succubus or Incubus. Though, that doesn't mean they can't adopt a human child to raise as their own. And you character can double as a teacher and someone whose job it is to bring humans from outside to feed the students.
Also, since there is a growing interest, let's go ahead and get a head count on what type of character a player is wanting to play. Just a couple of things to keep in mind if you are wanting to play as a student.
If you are wanting to play a shy virgin who has no clue what sex is or doesn't know what a penis is, then you are better off playing as a human who gets invited into the school. In this world, all the Succubi are sexual beings and want to have sex. Succubi can come in all shapes and sizes, even short and petite, but they must have physically mature bodies of teenagers age 16 and up.