Maybe it's not just the vampire houses? Maybe there's a series of residential houses that end up targeted and it just happens that the Kuran household is one of them? I'm just trying to think of a way for all the vampires to play. I know I've wanted to be able to get in on the vampire event.
We MIGHT be able to say in Zero's case, that he was running low. He goes through like...a bottle a day. We'd have to poke her about that though. (and I don't want to speak for what someone else's character will and won't do in regards to Gluttony too.