Well your father's father is your Grandfather. And it depends how your uncle is related to your grandfather. Your uncle could be your grandfather's son, or your grandfather could have a sibling who's child is your uncle- which would make him your Grandfather's nephew.
Your father or mother's uncle is your grand uncle. This person may also be called your great uncle.
You are his grand niece or grand nephew, depending on your sex.
Assuming we are talking direct line, your uncle is a sibling to one of your parents. His uncle is also an uncle to one of your parents and therefore your grand uncle.
The son of your Uncle's son is your uncle's grandson. Your uncle's grandson is your first cousin, once removed.
If he is your uncle by blood, his uncle is likely to be your great uncle. As to be an uncle it has to be a parents sibling. His parents would be your grandparents. So any of your grandparents siblings are typically called great uncles/aunts
The English language has no specific term for a relationship between your uncle and your wife. Your uncle will usually call her "my nephew's wife" and she can call him "my husband's uncle."
Joseph Stalin
Your grandmother's brother is your parent's uncle. The uncle's child would be your parents first cousin. You would be second cousins.
Your parents are great aunt and great uncle to the children of your first cousin.
Your great uncle
No, I think your consent would be required regardless of relation.
Your daughter is your uncle's grand niece.
Your Uncle's son is your first cousin.
There is no relation between you, and your biological Uncle's wife's sibling's daughter. Your Uncle's wife is technically an "Aunt in law", though as routine courtesy is simply called "Aunt". Her brother/sister, if your family and her family are that close, could be regarded as an "Uncle/Aunt in law", as a stretch. Thus the daughter of him/her could be thought of as a "cousin in law" to you. But this is all a matter of courtesy, there is no biological or legal relation.
You grandson is great great nephew to your uncle. You uncle is great great uncle to your grandson
You grandson is great great nephew to your uncle. You uncle is great great uncle to your grandson
Your grandfather's brother is your great uncle and your parent's uncle.
uncle
Assuming we are talking direct line, your uncle is a sibling to one of your parents. His uncle is also an uncle to one of your parents and therefore your grand uncle.