I've been reading the spanish translation (these are up to date) and yep, I think your theory is right. It was so hard to read, I feel so bad for Minjae ))):
Where can I read the Spanish translation
In TMO, tuMangaOnline
I think, the bashing head is more like a deal between 1st son and Minjae.
It was so Minjae can get away from the SA.
Afterall, it was after that incident that Minjae got sent to overseas.
There's a chance that Minjae was gonna tell 2nd son about everything, so 1st son made a deal.
2nd son is obsessed with 1st son.
and 1st son is obsessed with 2nd son.
1st son want to make sure 2nd son stay as this "great heir who have no blemish".
So if the chairman got caught doing this shit, that will become the "blemish" in 2st son's life.
And 1st son really don't want that.
yeah, just got caught up to the raws and you're right. i think that was definitely easier to swallow than what i theorized lmao. i just need minjae to get his happily ever after
this sounds like a long shot but this is my theory: that not only is the chairman an abuser but also a pedo and pulled a leonardo dicaprio once he realized the eldest son was "too old for him" and was going to start abusing the second brother next. to protect his only younger brother, the eldest suggests to the chairman to adopt minjae, who's younger than the both of them. if minjae had found out that the reason he's going through this abuse is because of the eldest son, it would explain why minjae bashed his head with a vase (?).
also in the scene where the eldest hugs minjae to sleep, he says, "just close your eyes and you'll eventually fall asleep. that's what i did". minjae realizes, as an adult, that that hug was never meant to be "for him" because those were not words of comfort, but words of advice. despite it being his own suggestion, i think the eldest feels a sense of guilt/responsibility for being the cause of abuse for minjae because he forced the abuse to skip right over the second son to target the youngest.
anyway, the second season has around 3 or 4 chapters out right now about the time minjae was adopted into the family but i understand none of it lmao. excitedly waiting for the eng translation!!