Your great grandmother's great great granddaughter could be your:
You granddaughter is a great great niece of your aunt. Your aunt is your granddaughter's great great aunt.
Your great nephew and your granddaughter are second cousins to each other.
Great neice
No. The sister is a relation, and her husband is an in-law. The husband's brother is no biological relation either. Therefore, the great granddaughter of the husband's brother is not a relation.
Great niece
Your sister's daughter is your niece. Your sister's granddaughter is your great niece Your sister's granddaughter's daughter (your sister's great granddaughter) is your great great niece. You are her great great aunt, if you are a woman, or her great great uncle, if you are a man.
You and the granddaughter of your great grandmother's first cousin are third cousins, once removed.
Your granddaughter and your grandniece are second cousins or third cousins to each other
WHAT relationship* is your Gramps to your great granddaughter? pretty tricky but (distant sisters one off)
Fourth Cousins, twice removed
The great great grand daughter would be my cousin sister.
Your brothers granddaughter is your grandniece.