@Ipex yea they could, but if they think he is gone, and has no contact with them, then what is the point. Just for their sick pleasure? I forgot a couple things about this manga, but i don't remember them being that way. And I don't really understand what you mean about attachment.
Idk about that. I think if he frequently met up with them, the people chasing the vampires would go after his family in order to catch him. But if he just watches from afar and his family doesn't know that he is there most of time, I do not think that would be an issue.