Humans form close bonds with siblings, but they are platonic rather than romantic or sexual. In the case of humans, it's a taboo beacuse genetic defects are common when people produce offspring with close relatives. Vampires don't have that problem, especially not purebloods. It might still be somewhat of an issue for common vampires. I haven't researched it that far.

[She kind of prefers that single room that she's got, but...this would be helpful.]

If you haven't found someone to be your roommate within two weeks, I'm certain that Kaname would approve of me.