cousin
You are his first cousin.
If your sister had a son, then he is your nephew.
Your fathers brothers are your uncles. You are their nephew, or niece.
Your nephew's child is your great niece (if a girl) or your great nephew (if a boy).
The English language has no special name for a nephew's wife and does not consider you to be related to you. You would simply call her "my nephew's wife."
You are your nephew's uncle if you are male, and his aunt if you are female.
Your mother's nephew is your First Cousin.
Either nephew or nephew in law.
My sister's son is my nephew.
Nephew
Nephew.
Nephew...