Your father's great grandson could be your grandson, or your great nephew.
Great Uncle.
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 grandson is your sister's great nephew and she is his great aunt.
great great nephew and u wud be a great great aunt... i think :)
The great grandson of your great grandfather's brother is your third cousin
Your grandson and your great nephew are second cousins to each other.
The great grandson of your sister is your great great nephew. You are his great great aunt or great great uncle.
Your great great uncle's great great grandson is your third cousin once removed.
Great Grand Nephew
You are their great aunt/uncle.
She would be his Great Aunt