I am looking for a yaoi with two brothers that share a mom, but not a dad. The brothers then get into a gang after the oldest rapes the youngest. The manga stars with a boy trying to rescue the new boy toy to the oldest brother. The boy toy looks like their mom. The oldest has blond hair and the youngest has black hair. Hope this made sense ╮( ̄▽ ̄)╭
Ive only skimmed this but I think it’s the one you’re looking for; sorry if it isn’t, I’m only guessing https://www.mangago.zone/read-manga/yonin_no_nibiiro/
I will Murder ( ̄へ ̄)