If your sister-in-law is the wife of your brother, she is the mother of your brother's son. Her son-in-law would then be the brother-in-law of your brother's son.
If your sister-in-law is your spouse's sister, her son-in-law is not related to you or to your brother's son.
Your son would be the uncle of his brother's son.
your second nephew
your cousin
They would be cousins, once removed.
If your niece's is by your sister but the brother is by your sisters new husband & another woman there would be no blood relation. If not then he's the nephew
Hades and Zeus are brothers; Hercules is a son of Zeus and, as such, a nephew of Hades.
basiclly there called brothers .-.-.-.-.-.-. basically* for one... and two no, they wouldn't be called brothers. If it was their parents sons then yeah, but if it's the sons of brothers then they'd be cousins. That's practically like saying one brother got married and had a son, then the other did too and had a son as well. The relation of the sons would be cousins.
Your son and your niece are first cousins.
Your Uncle's son is your first cousin.
Your nephew's son is your great nephew.
Your son and your niece are first cousins. Your son and your niece's son are first cousins, once removed. Your grandson, or granddaughter, and your niece's son are second cousins.
Your nephew.