YOU SAID:
You are my sisters son
INTO JAPANESE
あなたは私の姉妹の息子です
BACK INTO ENGLISH
You are the son of my sister
INTO JAPANESE
あなたは私の妹の息子です
BACK INTO ENGLISH
You are my sister's son
INTO JAPANESE
あなたは私の妹の息子です
BACK INTO ENGLISH
You are my sister's son
You've done this before, haven't you.