
Honestly, my gut feeling tells me they had different mom's and there was something about them but that's just my guess.
All we know is Hyuk (the middle one) was the one the chairman actually liked. He's a pedophile who preyed on his own eldest child (Jungwoo). He probably likes them young and easy to overpower so he began to target Minjae after adopting him too.

- The (oldest brother)Jungwoos mother took money from president, exchange she would be quiet about that Jungwoo isnt blood related to Hyuk. You could say his own mother basically sold him to president. He was taken at young age and being abused since he was a little kid. He is being abused constantly and this is Probably the reason he was in bed all the time. He already has weak body and r*pe Probably damaged his body too. Child body, after all.
- Jungwoo once said that Hyuk is a present president gave him. Most likely, Hyuk is his real son, considering how much their looks are alike. Since he is genius, he was presidents favorite child. So he wasnt sxually abused and he had no idea what happenned to other siblings.
- Minjaes family died so president adopted him. Probably because Jungwoo became "too old for his taste" so he took another child to abuse. He r*ped Minjae that one night and thanks to Junhwoos plan, next day he got out of the house.
I am confused. Did the father assault the oldest and youngest son but not the middle one? Could someone explain?