Technnically, she is not related as you do not share a common ancestor. She would refer to you as Aunt and she is your niece.
Whether he is your first, second or fifth husband, his niece is your niece while you are married to him.
that would be your niece or if you want to be fussy then your niece in law!
No. Your wife's niece is also your niece, but the husband of the niece is not related to you or to your wife.
What is my godfathers niece to me
Your niece's brother is your nephew.
either your niece's husband, or your nephew, or your nephew in law, etc
Your son and your niece are first cousins.
Nothing. Your niece in law. Your brother in laws niece.
your niece
cousins
Your Aunt's niece is you (if you are female), your sister, or your First Cousin.
Your brother's daughter is your niece. Her daughter is your great niece.
You aren't related. You do not share a common ancestor.