Your uncle's son is your (first) cousin.
great uncle
His great uncle
Your uncle's son is your first cousin.
It means you have (or had) at least two uncles and at least two great-uncles, and that is all it means.
Your brother's daughter's daughter is your great niece.
They are your Uncles and or Aunts.
your uncles son is your cousin
It could be your son. It could be your nephew as well. It could be no relationship to you at all. The question is do you share a common ancestor? If you do not have a common ancestor, you are not related.
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.
Your cousin in law
If her son is from a previous relationship, then he would be your step-son.
I believe they would be great aunts or great uncles.