The grandson of your great great great great great uncle is the second cousin of your great great grandparent, and your second cousin, four times removed.
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 great great uncle's great great grandson is your third cousin once removed.
Great Uncle.
You are their great aunt/uncle.
Great great aunt/uncle. To your niece, you are the aunt/uncle, to her child you would be the great aunt/uncle. So you would then be the great great aunt/uncle of her child's child (her grandson)
The great grandson of your sister is your great great nephew. You are his great great aunt or great great uncle.
She would be his Great Aunt
You and your uncle's grandson are first cousins once removed.
The son of your Uncle's son is your uncle's grandson. Your uncle's grandson is your first cousin, once removed.
You and your great uncle's grandson are second cousins.
Your father's great grandson could be your grandson, or your great nephew.