Aunts usually address their nieces by name
That's easy cousins.
Your aunt's brother is either your father or your uncle. If you are a girl, you are always your aunt's niece.
You are your neice's aunt, your neice's children's great aunt, and your neice's grandchildren's great great aunt
Your niece in-law, or your niece by marriage.
Your niece will call you her aunt or uncle.
Great great aunt/uncle. To your niece, you are the aunt/uncle, to her child you would be the great aunt/uncle. So you would then be the great great aunt/uncle of her child's child (her grandson)
You would be her aunt. She would be your niece.
you would be her aunt and she would be your niece
You are the great-great-aunt/uncle to your niece's granddaughter. This means that your niece's granddaughter is your great-great-niece. The term "great-great" signifies that there are two generations between you and your niece's granddaughter.
A DNA comparison between an aunt and her niece would sho that they are related, but not as closely as siblings.
Yes, your niece's daughter is your grand niece. You are her great aunt or great uncle.
She would be your niece, and you would be her aunt or uncle.