Your great grandfather's sister is your great great aunt. Her grandchild is your parent's second cousin and your second cousin, once removed.
Your sister would be her great aunt and she would be your sisters great niece.
Your great uncle's grandchild is your second cousin.
Your great great grandfather.
Your great grandmother's sister is your great great aunt. Her great grandchild is your third cousin.
He would be his great great great uncle
Yes, along with your grandfathers' sisters, if any.
Your great grandfather's half-sister is your great great aunt, the same as his full-sister is.
Your great grandparents brothers and sisters are your great uncles and great aunts.
Great neice
nothing
Your child and your sister's child share a common grandparent and are first cousins. Your grandchild and your sister's grandchild share a common great grandparent and are second cousins. There is a generation out of synch, so they would be second cousins once removed.
They would be great nieces or great nephews.