Schizophrenia is basically a gamble of bad mental health genetic passed down through your bloodline. In the brother's case, it looks like it definitely came from the mother side. The Mom is shown to also be a bit crazy, from the few times she lost her baby coupled with miscarriage here and there. The grandmother's superstition didn't help her delusion either.
As far as I can tell the story subtly tried to show the mother's influence in this since the very beginning. How the brother needed help, but because the mom refuses to see past her sweet little boy it ended up destroying the brother and took the entire family with it. If he had gotten help since the beginning I think things wouldn't have gotten so bad. After all we still see him interacting normally from time to time with his sister when he can be normal.
For all I can say, I genuinely genuinely feel bad for the brother. He couldn't get better because his family basically treated him like trash throughout his schizophrenic episodes. The sister, while she was the victim through the story, was also a perpetual threat to his hallucinations, she used violence and abuse him when he's experiencing an episode he isn't consciously aware of. But it's neither him nor her fault.
I think the story is warning us how ignorant is why mentally killed people get to that point.
I read somewhere this illness might cause by genetics and environment and many complex cause, but in this story do you think it might be because of the stress of the mom? I mean she does go through some bullshit back then (not defending her) but seriously i need to know more whats the cause of his mental illness. Is it stress ? Is it because his parents forced him to go college ?. Anyway i feel bad for the mc so much :((( she been through a lot , glad she got the happy ending she deserve and glad the father got his redemption arc. The mom is just erhh.......