They would be first cousins once removed.
Your great aunt's children are the first cousins of your parent.
You Aunt is you grandson's Great-Great Aunt. Your grandson is your Aunt's Great-Great Nephew.
Your great-great aunt is your daughter's great-great-great aunt.
Your great aunt is your daughter's great great aunt. Your daughter is your great aunt's great great niece.
Great Aunt to Great Niece.
Your great aunt is either your father or your mother's aunt.
The great aunt is the great niece's baby's great-great aunt.
Your great aunt's grandson is your second cousin.
She would be your great aunt.
You are your neice's aunt, your neice's children's great aunt, and your neice's grandchildren's great great aunt
Your aunt is great great aunt to your son's daughter (your granddaughter). Your granddaughter is your aunt's great great niece.
The grandchild of your great aunt is your second cousin.
Your great aunt's great grandson is your second cousin, once removed.