I am sure that brother is fucking that step sister lol

Well i don't think so. That blond girl is regarded as their real family because she looks like mc's mother. Her father married that bitch mother because she looks like her mother

Quite possibly, yeah. Or at least trying to. She probably falls in love with the male lead of the story or something and the brother like the loser he is gets rejected with the teary typical "we cAnT...!"