YOU SAID:

I am the father of your mother of your sister.

INTO JAPANESE

私はあなたの妹のあなたの母親の父親です。

BACK INTO ENGLISH

I am your mother's father of your sister.

INTO JAPANESE

私はあなたの妹の母親の父親です。

BACK INTO ENGLISH

I am the father of your sister's mother.

INTO JAPANESE

私はあなたの妹の母の父です。

BACK INTO ENGLISH

I am the father of your sister's mother.