Ilhoon has so many posable parents I think they really all are his parents

GTOP, JunSeob, GSeob, ToJun, GJun, TOPSeob, GJoon, JoonMir all look like they could be his parents I've even heard JunSeung and 2Seung (SeungRi x HyunSeung) could be

so I think think they all just got together, ed and made him

yes that's what happened! That's how we got BTOB's Ilhoon