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.
Your uncle-by-marriage's nephews might be you and your siblings. You are your uncle's nephew or niece.They might be the children of your aunt's siblings (your aunt being his wife), in which case they are your cousins.If they are your uncle's nephews by virtue of being children of his siblings, they are no relation to you at all.
The children of your husband's siblings are your nieces or nephews. Their children are your great-nieces or great-nephews.
You are their great aunt/uncle.
3rd cousin
2nd uncle I believe
Nephews and nieces
Your borther-in-law's children are your nieces and nephews. You are their uncle or aunt, as is your spouse.
Cousin in Law
He would be his great great great uncle
They would be great nieces or great nephews.
You would be his Great Uncle and he would be your Great Nephew.