I just set aside that they're step brothers so I can fully enjoy reading this

they are not related they are not related this isnt weird ...i repeat to myself TnT

I genuinely do not understand how that skeeves people out. They did not grow up knowing each other as brothers, it's not like it was an established sibling relationship from a super young age. They were forced into each others' lives as teenagers. Their parents getting married doesn't mean they see each other as family, they're just two kids whose lives got turned upside down.