YOU SAID:

My mother told my sister that she was my brother's niece.

INTO JAPANESE

母は姉に、兄のだと言った。

BACK INTO ENGLISH

My mother told her sister that she was his brother.

INTO JAPANESE

母は妹に自分が彼の兄弟だと言った。

BACK INTO ENGLISH

Mother told her sister that she was his brother.

INTO JAPANESE

母は妹に自分が彼の兄弟だと言った。

BACK INTO ENGLISH

Mother told her sister that she was his brother.