You are your nephew's uncle if you are male, and his aunt if you are female.
If your sister had a son, then he is your nephew.
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."
Your mother's nephew is your First Cousin.
Either nephew or nephew in law.
My sister's son is my nephew.
sweety
Nephew.
Nephew
Nephew...
Nephew
Your nephew.