In English there is no relationship name for this extension. One must name the relationship as you phrased it. In English, this is not a proper legal term in relation to you.
You brother is your grandchildren's great uncle or granduncle.Your grandchildren are your brother's grandnieces and grandnephews
There is none, as there is no actual relationship.
He is his brother-in-law.
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.
I'd get his phone number and dial it. And use his first name. There is no relationship. He is your brother-in-law's brother.
Your brother's children would be your nieces and nephews.
Sister-in-law. same as your brother's wife.
neice
Nephew
Your son's wife is your daughter-in-law. Her brother is your son's brother-in-law, but the English language has no word for a relationship between you and him. You are not considered to be related to him.
RODNEY
Use of their name is appropriate. If you have to explain their relationship, they would be your son's wife's brother, or your daughter-in-law's brother.