Your great aunt is the sister of your great grandparent. Her granddaughter is your second cousin and her great granddaughter is your second cousin, once removed.
your 2nd cousin
First cousins, twice removed. Aunts daughter is your cousin. Aunts daughters daughter is cousin once removed Aunts daughters daughters daughter is cousin twice removed.
No relationship at all, you don't share a common ancestor.
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.
They would be your second cousin. Your great aunt is the sister of one of your grandparents. Your parents and the granddaughter's parents are first cousins.
Your sister is the great-aunt (also written great aunt) of your granddaughter.
your niece
Your uncle's great granddaughter is your first cousin, twice removed.
Your niece's 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).
great aunt
Your aunt is great great aunt to your son's daughter (your granddaughter). Your granddaughter is your aunt's great great niece.