I HAVE A THEORY- So, i'm pretty sure they have triplets and all of them is theirs, and maybe, just maybe, Idea can only sense Hwa's blood in one or two of the children because those kids might have more of Hwa's blood and a little bit of Hyung's blood in them and the other one(s) might have more of Hyung's blood and a little bit of Hwa's blood. BUT, THAT'S WHAT I THINK, IT'S ONLY MY OPINION-
why does the white hair boy look like Zen from Mystic Messenger? Like huh?? Did the author suddenly decide to drag Zen into their story, i can't- But, if he tries to ruin our babies relationship, i'm going to bring weapons-