Your great aunt's son is your parent's first cousin and your first your cousin, once removed.
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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.
your cousin
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.
your niece
Your first cousin.
Your Aunt's first cousin may be your second cousin, onve removed or may be no relation to you at all.
great nephew
Your grandfather's daughter-in-law could be your mother or your aunt by marriage. Your mother's brother is your uncle and his son is your first cousin. The brother of your aunt by marriage (the wife of an uncle) is not related to you, and neither is his son.
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.
to make it easier lets say ' aunts son' so that is your cousin