Your borther-in-law is your grandchildren's great uncle. They are his great nieces and great nephews.
You brother is your grandchildren's great uncle or granduncle.Your grandchildren are your brother's grandnieces and grandnephews
aunt
The grandchildren of your grandmother and the grandchildren of any of her siblings (including of her brother) are second cousins to each other.
He is brother your brother in law.
There is none, as there is no actual relationship.
Your sister-in-law is either the sister of your spouse or the wife of your brother. The parents of the sister of your spouse are also the parents of your spouse and so are your mother-in-law and father-in-law. The parents of the wife of your brother are not related to you.
Your brother-in-law is either the husband of your sister or the brother of your spouse.Where your brother-in-law is the husband of your sister, there is no relationship name in the English language to describe his brother's relationship to you. However, in that situation your brother-in-law's brother is your sister'sbrother-in-law.Where your brother-in-law is the brother of your spouse, his brother is also your brother-in-law.
Your wife's brother is your brother-in-law.
Unless your brother-in-law's brother is your husband, there is no direct relationship.
Brother-in-law
Your brother's wife is your sister-in-law. The English language has no relationship term for the brother of your sister-in-law. He is not considered to be related toyou, although he is your brother's brother-in-law.
Your sister-in-law's husband is never your brother-in-law. He can be your brother, when your sister-in-law has that relationship to you because she is married to your brother. You could also have a sister-in-law who is the sister of your spouse. But then her husband is not related to you.