You would call your daughter's son by his name ex: Hi Jack.
His name.
Your daughter is your sister's niece. Your daughter's son is her great nephew.
daughter...daughter in law.
daughter in law
daughter in law
Your grandson.
Your son-in-law is your daughter's husband.
Your grandson.
you can call him your nephew if you are mom's daughter's sibling or if you will be the mom you can call him your grandson.
Your father's brother's son is your first cousin and your daughter's second cousin.
The brother of a daughter in law is the son in law.