If your brother-in-law is your spouse's brother, then his sister's daughter is your spouse's niece, and your niece, too.
If your brother-in-law is your sister's husband, then his sister is not related to you, and neither is her daughter.
your brother's daughter is you niece
brother's daughter relation
Your brother's daughter is your niece. Her daughter is your great niece.
Your brother's son or daughter is your nephew or niece respectively.
brother-in-law
Your brother or sister's daughter is called 'your niece.'
Your mother's brother is you uncle and your daughter's great uncle. Your daughter is his great niece.
Your sisters daygter is your neice!
Your grandfather's brother's daughter is your first cousin, once removed.
I guess you will be her uncle. Consider this case.. You have a brother and he has a daughter.. Your daughter will be a sister in law to your brother's daughter.
3rd cousin I think:-)
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.