Yes, but I think the brother also genuinely enjoys taking things from Jaeyi because he's a shit. You can blame bad parenting for a lot, but at some point as an adult your choices fall only on you. He's spent enough time in the world to learn how to be a better person if he wanted to. Same goes for Jaeyi and how he treats people that aren't Ideum, but I don't guess he's really hurting anyone just by being an ass.
also yes, they let oldest to do whatever he wanted from small age and he still does whatever he wants and same goes for Jeayi, but for Jaeyi his parents weren't there to teach him, they were too busy with eldest and his sickness.
it will hurt like b!tch when they separate , i just hope author won't drag it unnecessary long.

i really want angst to come so they can be together all clingy and everything but i don't want Ideum to hurt and Jaeyi too.
All that brother against brother situation is only because of poor parenting , poor boys.