kinda getting now(?)

now everything kinda makes sense.. so both brothers were experimented and that's why they act inhuman. i thought the little one was their biological child but he's not? if that's the case it makes the parents sus in my eyes too. also i still don't get the obsessive behavior of seme like why he's so hung up on his bro like crazy since childhood. did they share a past or something in the lab? i have too many questions and hoping to find them answers