El hijo de mis padres que no soy yo es mi hermano.
Explanation:
El hijo de mis padres que no soy yo es mi hermano. This means: he's the son of my parents but he's not me. He's my brother. "Mi tío" means "my uncle". He is my mother's or my father's brother. Or he could be married to my father's or mother's sister. "Mi primo" means "my cousin". He's the son of my uncle and my aunt. "Mi sobrino" means "my nephew", he es my brother's son.
