Your sister's daughter and your son are first cousins to each other.
Your daughter's son is your grandson and you are his grandparent.
Your son and your sisters child are first cousins. The granddaughter is out of synch by a generation. That will make them first cousins once removed.
Your aunt is great great aunt to your son's daughter (your granddaughter). Your granddaughter is your aunt's great great niece.
Publius.
JULIA CARSON did not have a daughter she had a son name SAMUEL CARSON and CHRISTOPHER CARSON
Your younger brother's wife's sister's daughter would be your son's cousin.
Your sister's son is your nephew.
Grandaughter.
daughter-in-law
Son-In-Law
Neice or nephew no dummy its nephew
Daughter is the opposite of son.
Your sister's son is your nephew. Your son's daughter is your granddaughter. Your son and your sister's son are first cousins to each other. Your son's daughter and your sister's son are first cousins once removed to each other. Your grandchild and your sister's grandshild are second cousins to each other.
Your son's wife is your daughter-in-law. Her brother is your son's brother-in-law, but the English language has no word for a relationship between you and him. You are not considered to be related to him.
Your daughter's son is your other daughter's nephew and she is his aunt.
Your daughter's son is your grandson and you are his grandparent.
Your son's brother in law is likely your daughter's husband. If that's the case he's your son in law.