They would be cousins.
Your brother's son or daughter is your nephew or niece respectively.
No, your son-in-law is married to your daughter and his brother is not your son-in-law, but simply your son-in-law's brother or your daughter's brother-in-law.
Your brother's son is your nephew. So his daughter would be your grand niece.
If your daughter's brother-in-law is the brother of your son-in-law he is not otherwise related to you.If your daughter's brother-in-law is husband of her sister, then he is your son-in-law.
Your father's brother's son's daughter is your second cousin.
Your brother would be your son's daughter's great uncle and your son's daughter would be your brothers great niece! Hopefully that makes sense :)
Your son's wife is your daughter-in-law. Her brother is not related to you, but is your son's brother-in-law.
Your son-in-law's brother's son is not related to you, but is your daughter's nephew.
A son
Your brother's son's daughter is your great niece, and you are her great uncle or great aunt.
Your brother would be your son's daughter's great uncle and your son's daughter would be your brothers great niece! Hopefully that makes sense :)
The brother of a daughter in law is the son in law.