If your sister-in-law is the sister of your spouse, her brother is your brother-in-law (or your husband if you are a woman).
If your sister-in-law is the wife of your brother, then her brother is not related to you.
No relation
Brother-in-law
brother
Brother in law
Your brother or brother in law
your brother's daughter is you niece
your brother
He's your brother-in-law.
Your niece's brother is your nephew.
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.
brother's daughter relation
They are brothers in law