YOU SAID:

i have a dad from my mom.

INTO JAPANESE

私はお母さんからお父さんがいます。

BACK INTO ENGLISH

I have a father from my mother.

INTO JAPANESE

私には母の父がいます。

BACK INTO ENGLISH

I have my mother's father.

INTO JAPANESE

私には母の父親がいます。

BACK INTO ENGLISH

I have my mother's father.