Your grandmother's nephew is first cousin to one of your parents and first cousin, once removed, to you. His child is your second cousin, so his grand daughter is your second cousin, once removed.
If she's not your mother, that would make her your Aunt.
go ahead if you want to marry your aunt
Your sisters daygter is your neice!
Your sister's son is her grandson and your great nephew. Some use the term "grand nephew."
If you have no siblings but your daughter has an uncle, he is the brother of your spouse, your brother-in-law.
If your great great grandmothers were sisters, your common ancestors are your great great great grandparents. That makes you 4th cousins.
Your grandmother's sisters are your Great Aunts.
Your daughter and your sister's child are first cousins. Your daughter and your sister's grandchild are first cousins, once removed.
Your sister is great aunt to your daughter's child. The child is your sisters great nephew (if a boy) or great niece (if a girl).
The relation of the mother;s sister to daughter is niece-aunts.
Yes, along with your grandfathers' sisters, if any.
There is no relation between you and your grandmother's cousin-in-law's grandson.