Shouldn't omegaverse have a kind of family bond thing in their blood which makes pheromone...

I'm going to assume their step-brothers for now.

In the animal kingdom do siblings see each other as siblings or just as males and females? Omegaverse is loosely based on animal hierarchies and relationships....his parents may be bonded omega x alpha so he'd be safe from them but not necessarily his full or step bro. I've seen a manga where an alpha twin sexed his omega bro during his heat bc his rut was so intense--he even bit his brother and paired with him. I have looked ahead at the raws if you want a spoiler but it may be more fun to enjoy the suspense.

Animals very rarely mate with close blood relations. They usually have systems in place that naturally prevent it. Close genetic coupling makes weak offspring with more genetic mutations and increased chances of birth defects and genetic disease.

Interesting article about this... https://www.thenakedscientists.com/articles/questions/do-wild-animals-avoid-incest

Which manga is that? ..asking for a friend

It depends how the author creates the omegavers world. I've also read a manga, where the younger omega brother got raped by his brother and got pregnant...

It's been a while but I think it was this one...
http://www.mangago.zone/read-manga/ai_to_makoto_moriyo/

Guess you haven’t been raised around animals. They really don’t give two shits whether or not they’re related or same sex.

Which one?

http://www.mangago.zone/read-manga/ai_to_makoto_moriyo/

Bo, I'm referring to the comment about the brother getting his brother pregnant

http://www.mangago.zone/read-manga/sayonara_koibito_mata_kite_tomodachi/
The main story isn't about that, it's part of the past
But in this manga the whole omegavers stuff is kinda messed up...

Sorry was wrong on that, they just paired.