YOU SAID:

my nan is my gran if my brother is my mother

INTO JAPANESE

私の兄が私の母なら私のナンは私のおばあちゃんです

BACK INTO ENGLISH

If my brother is my mother my nan is my grandma

INTO JAPANESE

私の兄が私の母なら私のナンは私のおばあちゃんです

BACK INTO ENGLISH

If my brother is my mother my nan is my grandma