Your son-in-law's brother's son is not related to you, but is your daughter's nephew.
my brother doesn't have a son.
Your son would be the uncle of his brother's son.
the son would be the nephew
He had three brothers; he was the oldest son.
Nephew
The son(s) of your parents.
Nephew...
Nephew.
Great uncle / Great nephew
of course.......................MAIDEN
nephew
his brothers and son and jason