I'd like to see how one of Moka's sisters would react to knowing their younger sister injected blood into a human.
Actually, I have this funny image of Moka's father and her two older sisters stalking her and Tsukune to make sure things don't get out of hand when they're together; hiding in bushes and around corners like Mizune. I can see Moka's father being an overprotective dad who is anugished by the thought of his baby dating.
And I speak from experience when I say that big sisters can be pretty protective of their younger sisters when it comes to boys.
As for Kokoa; is there a certain age where a vampire aquires their true powers or is it something they're born with? Because she's only a year younger than Moka and she's almost as strong, but she hasn't shown any real vampire traits of her own (silver hair, red eyes, etc.). Maybe her mother wasn't a vampire.