Your Grandmother's sister is your great aunt. Her grand daughter is your second cousin and her great granddaughter is your second cousin, once removed.
If your great great grandmothers were sisters, your common ancestors are your great great great grandparents. That makes you 4th cousins.
WHAT relationship* is your Gramps to your great granddaughter? pretty tricky but (distant sisters one off)
The relationship is that of a great great great grand uncle and great great great grand niece
Your grandmother's sisters are your Great Aunts.
Your sister is her great grandaunt.
Your brothers great granddaughter is your great great niece.
Your granddaughter is your sister's great niece. Your sister is your granddaughter's great aunt.
My ancestors
Yes, along with your grandfathers' sisters, if any.
Your sister's granddaughter is your great niece and you are her great aunt (if you are a woman) or great uncle (if you are a man).
Great neice
Your great great grandmother's sister's great great grandson is your third cousin, twice removed.