Your aunt's son and your children are first cousins to each other.
Your mother's brother is your uncle.The children of your aunts and uncles are your first cousins.
He would call your aunt his great aunt. In informal situations, great aunts are sometimes called, simply aunt.
He would call your aunt his great aunt. In informal situations, great aunts are sometimes called, simply aunt.
A nephew is a cousin to his aunt's son.
Your son and your aunt's son are first cousins once removed to each other.
great nephew
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Your grandfather's children are either your parents or aunts or uncles.
Assuming that "his aunts" have reached the age of majority and that "your son" has a passport with the VISAs required by Morocco for citizens of "your son's" country, there should be no issue.
Your aunt's daughter is your first cousin, and her son is your first cousin, once removed.
Aunts.
They'd be your cousin.