YOU SAID:

My sister has the same dad as me, and he is my dad's dad.

INTO JAPANESE

私の妹は、私と同じお父さんと彼は私のお父さんのお父さん。

BACK INTO ENGLISH

My sister, my dad and he's my dad.

INTO JAPANESE

私の妹、私の父と彼の父。

BACK INTO ENGLISH

My sister, my father and his father.

INTO JAPANESE

私の妹、私の父と彼の父。

BACK INTO ENGLISH

My sister, my father and his father.