YOU SAID:

I slept with the step brother of my friend's cousin's dad

INTO JAPANESE

友達のいとこのお父さんの義理の弟と寝た

BACK INTO ENGLISH

I slept with my friend's cousin's dad's stepbrother

INTO JAPANESE

友達のいとこのお父さんの義理の兄弟と寝た

BACK INTO ENGLISH

I slept with my friend's cousin's dad's stepbrother