There's no way Sihyun doesn't know his brother being abused (abandonment is abuse, ignoring your child is abuse, verbal humiliation and degradation is abuse). Actually, fuck MC too.
Basically Sihyun in chapter 23: "Brother I know you've been mistreated by our parents and I watched every scene unfold without doing anything, and now you finally crashed out. I'm happy!"
Done reading and I stand by my words. Fuck everyone except Namhyun and Jiseok (red haired friend). Kind mary sue characters, fuck them. They did mistakeS but is okay because they are nice. They did their mistakeS nicely. No character should be able to crash out on them because they are nice.
Having experienced it your entire life and then your crush said they wouldn't do the exact thing yet blaming Namhyun for that?? MC basically just proving Namhyun concerns right. I mean, yeah, Namhyun could just tell MC that. He basically at fault too in that. But the entire thing?? Was not his fault 100%.
Also fuck everyone associated with the family including the older brother, fuck him, fuck them.