your nan's sister is one of your parent's aunts. therefore, she's your great aunt x
Your mother's aunt's husband's sister is your mother's aunts sister-in-law but is not related to you. Her son is not related to you either.
The relation of the mother;s sister to daughter is niece-aunts.
child. The father is related to his sister which would be an aunt to this child, but the child s the aunts niece and this is their relation.
your niece
Your first cousin.
Since your mother and her sister have thesame aunts and uncles, your mother's sister's aunt is your grand aunt or, as some sat, your great aunt.
The common ancestor is your parents. Your children and your sister's children are first cousins. Your grandchildren and your sister's grandchildren are second cousins. Your great-grandchildren and your sister's great-grandchildren are third cousins.
Real sister, half sister, or step sister
sister in law.
Your sister's sister is your sister.
Your Aunt's first cousin may be your second cousin, onve removed or may be no relation to you at all.