Your husband's sister's son is your nephew, just as your sister's son is your nephew.
The son of your brother or sister is your nephew.It is your nephew
Your sister's daughter is your niece. Your sister's daughter's son (your sister's grandson) is your great nephew.
Your sister's son is your nephew.
Her name was Publius.
Your sister's daughter and your son are first cousins to each other.
The English language makes no distinction between an elder sister and a younger sister, or their children. Your sister's son is your nephew.
He would be your nephew.
If your sister-in-law is the sister of your spouse, her son is not related to your sister's son. If your sister-in-law is the wife of your brother, her son and your sister's son are first cousins.
I'd use their name. There is no official name for it. You do not share a common ancestor, so you are not related.
His sister's name is Carly...she has a son named Copper but I don't think she had ever been married.
Your sister's son is not related to your husband's sister's son, because they share no common ancestor.