Your uncle's son is your first cousin. He and your daughter are first cousin, once removed, to each other.
Your brother's daughter's daughter is your great niece.
First answer:that would be your second cousin. It is legal in the united states to marry them due to genetics Second answer:Your question is: "What is the relationship of your uncles son daughter to you?" If you are asking, "What is the relationship of your uncle's son and daughter to you?" they are your first cousins.If you are asking, "What is the relationship of your uncle's son's daughter to you?" she is your first cousin once removed.
great uncle
His great uncle
The grandchildren of any of your great uncles and great aunts are your second cousins.
Your daughter's son is your other daughter's nephew and she is his aunt.
your uncles daughter would be your cousin
Your uncle/aunt's son/daughter is an adult and you are still small, your uncle/aunt's daughter had a child, and that child will call you uncle. Uncles/aunts are your dad/mom's siblings.
Your uncles daughter would be your cousin.
your uncles daughter would be your cousin
Your daughter's son is your grandson and you are his grandparent.
2nd cousin.