great uncle inlaw
Your mother's brother is you uncle and your daughter's great uncle. Your daughter is his great niece.
Your mother's brother is your uncle. Any child of your mother's brother is your first cousin.
Your mother's son is you or your brother. Your mother's son's daughter is your daughter, or your niece. Your mother's son's daughter's mother is your wife, or your sister-in-law.
Your mother's mother is your grandmother.Your grandmother's brother is your great uncle.Your great uncle's daughter is your mother's first cousin, and your first cousin, once removed.
they are your cousin
Your cousin.
yes
2nd cousin
No.
If your brother-in-law's daughter is by your sister, she is your niece. If your brother-in-law's daughter is by someone else, she is genealogically not in your family tree.
In the English language relationship words make no distinction between younger or older siblings. Your mother's brother, whether younger or older, is your uncle and his daughter is your first cousin. His daughter is your mother's niece.
According to the chart used by courts and most genealogical societies, your brother's daughter's daughter would be your Grand Niece Reference: http://freepages.genealogy.rootsweb.ancestry.com/~gentutor/chart.html