it could either be your brother/sister or cousin
No.
Sisters, mother, aunts, grandmothers, nieces, cousins, etc.
With their children, nieces, and nephews.
Aunts usually address their nieces by name
your niece
Great-niece.
Second Cousin
I found the answer myself: Affinity ordinarily terminates upon the Divorce or death of the blood relation through whom the relationship was formed.
Your first cousin.
Nephews and nieces
your 2nd niece...!
If your great uncle married into your family some of his nieces and nephews are your aunts or uncles (or your parent) and some are not related to you at all.