Then you have a major problem
You would be second cousins.
Your child and your great nephew's parents would be first cousins. Their children would then be second cousins. And if they have children, they will be third cousins.
Your daughter and your sister's child are first cousins. Your daughter and your sister's grandchild are first cousins, once removed.
Your granddaughter and your niece's son (the grandson of one of your siblings) are second cousins to each other.
(1) Your niece is the daughter of your sibling (2) Your niece and your children are 1st cousins (3) Your grandchildren and your niece's children are 2nd cousins (4) Your g'children and your niece's g'children are 2nd cousins once removed
Your daughter's daughter is your grand daughter. Your nephew's daughter is the granddaughter of your sibling (your brother or sister) The grandchildren of siblings are second cousins.
Your child and your sister's child share a common grandparent and are first cousins. Your grandchild and your sister's grandchild share a common great grandparent and are second cousins. There is a generation out of synch, so they would be second cousins once removed.
Your grandfather's niece is your parent's first cousin. Her daughter is your second cousins and her granddaughter is your second cousin, once removed.
grandaughter
Yes
ben cousins
Grandaughter