Kyuhyun and his hyungs are bonded by blood, not bonded by blood like siblings do.  They share a same blood, they share same mortality, mortality that not as ordinary as humans.  They are human, they are blood-drinker vampire, they are in between.  Call them human, call them vampire, call them everything you want.  They came from different background but share the same blood of the king of vampire, they are 13 super brothers.