A grandson or grandchild, or remoter lineal descendant., A cousin., The son of a brother or a sister, or of a brother-in-law or sister-in-law.
Brother-in-law is a compound noun; a word made up of two or mare words that from a word with its own meaning.
brother in law
He is brother your brother in law.
If your brother-in-law is the brother of your spouse, he is not related to your brother. If your brother-in-law is the husband of your sister, then he is also your brother's brother-in-law
Your brother-in-law is either the husband of your sister or the brother of your husband. Your brother-in-law is not your husband's brother-in-law.
A relative, in general; especially, a descendant, whether male or female; a granddaughter or a grandson., A daughter of one's brother or sister, or of one's brother-in-law or sister-in-law.
If your brother-in-law is the brother of your wife, then his brother-in-law is you.If your brother-in-law is the husband of your sister, then his brother-in-law is you or one of your other brothers.Either kind of brother-in-law can also have brothers-in-law who are married to other sisters he may have. They are not related to you at all.
Your brother and your brother-in-law are not related. They can, of course, be friends. Your brother in law is married to your sister therefore he is your brothers brother in law also.
Your wife's brother is your brother-in-law.
The brother of your spouse is your brother-in-law.
Your sister's husband is your brother-in-law. The English language has no term for the brother of your brother-in-law. You would not be considered to be related to him.