You are his uncle, he is your nephew.
cousin
Your father's sister is your aunt and her son is your first cousin.
Your sister's son is your nephew His sons are your grandnephews, and his daughters are your grandnieces.
Well, it depends how close you are to your husbands family. If you really want to know they are cousins-in-law.
your second nephew
Your sister's son is her grandson and your great nephew. Some use the term "grand nephew."
Your sister's son is your nephew His sons are your grandnephews, and his daughters are your grandnieces.
Your sister's son is your nephew and you are his aunt (if you are female) or his uncle (if you are male.
They are sisters; both daughters of Rhea and Cronus.
Father or uncle
You and the son of your uncle are first cousins to each other.
If your niece's is by your sister but the brother is by your sisters new husband & another woman there would be no blood relation. If not then he's the nephew