A grandmother is your mother's parent.
An aunt is your cousin's mother.
Your mom is your uncle's sister.
Your brother is your cousin's brother.
My sister is my mother's daughter.
My grandmother is my aunt's mother.
My father's spouse is my mother.
If I have 2 brothers and 1 sister I have 2 siblings.
If there are three children in the family, they all have 2 siblings.
Your grandmother's parents are your great-grandparents.