I think I took it more as both sides misunderstanding each other. The sick brother viewed his younger brother as having more freedom to be healthy and just be a kid, he didn’t see how alone he was. Whereas the younger brother despite having that freedom was left alone a lot more because of it. The parents as well when put into a situation like that, you want to make sure the sick kid is well ok, it’s a lot of money and extremely draining. Even the broken toy, it was an accident but the sick kid overheard the younger brothers anger towards him so of course he thought in turn the younger brother wanted him to die. To start it wasn’t that the younger brother hated the older but it was just unintentional neglect. This is a very real representation of what can happen to kids in these situations. The older brother didn’t view it as him being more loved or anything like that, he was sick which would have made him feel pretty shit day to day. Even at the end of that chapter you can see he goes for the younger brothers magazine and what he wants, yes it’s shitty in the eyes of the younger brothers neglect, but in the eyes of the older brother he’s mad at the younger for having that freedom and still (thinking) he wanted him dead. It’s legit just both sides not getting 100% of something and in turn taking it out on each other. We can also see both sides extremely suck at saying their honest feelings. Like the younger turned into an avoidant lol.
Sorry for the rant lol
I don't get his brother. Yes, you were sick but you were the one who was more loved, more favored, more cared for — so why the fuck are you coming after your brother? Because he's never been sick? Well guess what motherfucker, he was never loved and cared for like you were and always had to give way to you. The least you could do is leave him alone, but no you just had to mess with his life too like he doesn't deserve a single peace.