There would be no relationship as you do not share a common ancestor. If your brother-in-law is married to your sister, then her daughter is your niece, her husband would be referred to as your niece's husband.
would it be a brother in law? not sure about this one! Is it your husband/wifes daughters brother?
would it be a brother in law? not sure about this one! Is it your husband/wifes daughters brother?
Your wife's sister's husband is your wife's brother-in-law, but is not related to you.
Your sister in law is your husband's sister or your brother's wife.
Your brother's daughters are your nieces
There are no laws about immoral activities such as infidelity.
You are not related as you do not share a common ancestor.
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.
Your wife's brother-in-law is either your brother or the husband of her sister. In the first case, her brother-in-law's brother is you or one of your other brothers. In the second case, her brother-in-law's brother is not related to you.
Your husband's brother - is your brother-in-law.
Since it would be your sister who had the child with her husband (your brother-in-law) then that would make their child your niece or nephew.
Your daughters husband is you son-in-law.