YOU SAID:

a brother from another mother

INTO JAPANESE

母親が違うだけだろ？

BACK INTO ENGLISH

Only the mother is different, right?

INTO JAPANESE

母だけが違うんですよね？

BACK INTO ENGLISH

Only my mother is different, right?

INTO JAPANESE

私の母だけが違いますよね？

BACK INTO ENGLISH

Only my mother is different, right?