brother-in-law
No relation...lol
I think it is appropriate to call him your brother.
No. The sister is a relation, and her husband is an in-law. The husband's brother is no biological relation either. Therefore, the great granddaughter of the husband's brother is not a relation.
He is of relation as a cousin-in-law.
sisters in law
Your cousin-in-law.
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
There is none.
Your husband's grandniece is your grandniece-in-law.
She is your sister-in-law.
He is technically no relation, as you do not share a common ancestor. He is your husband's first cousin once removed.
You are not related to your cousin's husband. He would simply be "My cousin's husband."