Idea did not see the personality split on Seolhyun.
Is just a tool to protect it's master (bloodline). He reacted because those babies are obviously Hwa's, but let's not forget that both of them are quite special in regards their race anyway.
The only one aware of this split personality is the child-version of Seolhyun in his mind and Ino (now Granpa after talking about it), that used hypnosis that leads to this split in the first place.
Let's not forget that Seolhyun is a mutant female lycan.
So Idea understanding those two personalities as babies is a big of a stretch. At least from the future chapters reviews I've read.
I honestly don't understand what your pertaining here, I'm quite lost XD (no anger and judgement. I'm just lost) But this reply of you us clearer than the other 2, I may say.
Idea is an existence that is lead by Blood Link and primitive instincts, so we can't quite understand what and how many he's pertaining to.
Anyway, I don't know If I'm right, but 3 babies will be good and UwU too
ヾ(❀╹◡╹)ノ~
Don't worry, I did not feel you were angry at all.
I'll try to explain the best I can:
1 - Like you've seen Idea is an existence, tool or power that Ybin uses. They have primitive instincts in order to protect its master. You're on the right path.
2 - Because of the nature of Idea, is quite unrealistic to misunderstand babies as personalities (confirmation in the Spanish translations). Its role at the moment is to protect the blood. So Seolhyun expecting Hwa's babies, automatically enable his protection.
3 - Personality split that Seolhyun has, is a result of Ino's hypnosis to help him survive the loss of his mark (Hwa's imprint).
4 - Seolhyun's a mutant female Lycan. Because his parents were both female Lycans (normal by the way). The nature of a mutant female Lycan is violent, ferocious and they usually kill their partners.
5 - The only ones aware of this split personalities are Ino and Granpa. Hwa knows Seolhyun is a female Lycan but isn't aware of the personalities.
6 - The issue that might kill those babies, at least might be the personalities, his lost memories, or even the species those babies might belong too. Because, if you remember in season 1, Hwagok almost died while giving birth to Hwa Lee, due to his vampire blood.
Anything else, I will wait for the future chapters
PS: English is not my first language, so I apologize for any confusion in my writing.
The only part the I understood was (I think? i don't know If I'm right) The three Idea is referring to is
(1) Seolhyun as a human male
(2) Seolhyun as a Lycan female
(3) Seolhyun and Hwa's Child
PLEASE DON'T LET THE CHILD DIE UwU
ANWAYS, INO IS VERY LOVED #-.-)