He is her nephew, and she is his aunt.
You sister-in-law is your son's aunt. the relationship consider age diff.if she is lower age what is his relationship.
Your sister-in-law in your son's aunt and he is her nephew.
A man is his sister's son's Uncle. A woman is her sister's son's Aunt .
Other than being your son-in-law's sister, there is no relationship.
Your sister's son is your nephew.
A man is his sister's son's Uncle. A woman is her sister's son's Aunt .
Your sister's daughter and your son are first cousins to each other.
Your son and your mother's sister are in a "Great Nephew/Great Aunt" relationship.
Step Nephew
Relationship sequence:You grandmother's sister is your great auntHer son is 1st cousin of one of your parentsHer son's son is your 2nd cousin
Your son and your mother's sister are in a "Great Nephew/Great Aunt" relationship.
Your daughter's son's son is your great grandson. Your daughter and your sister's son are first cousins. Your great grandson and your sister's son are first cousins, twice removed. Your great grandson and your sister's great grandchild are third cousins.