Your father's sister is you aunt.
Her son is your first cousin.
Her son's daughter (her granddaughter) is your first cousin, once removed.
Her father, unless the son and his sister have different fathers which would make him nothing to his son's sister.
Your sister's son, is your nephew.
Cousins
Your sister's son, is your nephew.
Your sister's son is called your nephew. You are his aunt (if you are a woman) or his uncle (if you are a man).
Your sister-in-law's grandson is your great nephew.
Your father's sister is your aunt. Her son is your first cousin. Her grandson is your first cousin, once removed.
No, because my father's sister (my aunt) does not have any sons, she only had daughters.
cousin
Your cousin.
Your Nephew
Your cousin