wait... bu-but they r half bothers(￣∇￣")

Oh, nono, theyre not. It's just in chinese, they called guys younger than them 'little brother' even if theyre strangers (=・ω・=)

Oh,, i just realised what you meant. Uhm you mean theyre step brothers right? Hehe my bad

They're not. He's calling him brother as way of calling someone older than him. It's normal in china.