John Adams, the second president, had children, one of whom became President.
The first President, Washington, was seemingly unable to father children.
George Bush had one son and a daughter who became president busch.
Your sister is your son's aunt. Your sister's daughter is your sons first cousin. Your sister's daughter's son (your sister's grandson) is your son's first cousin, once removed.
Your son and your niece are first cousins. Her daughter and your son are first cousins, once removed.
Your sister is your son's aunt. Your sister's daughter is your sons first cousin. Your sister's daughter's son (your sister's grandson) is your son's first cousin, once removed.
they have a daughter and son who married
Your daughter and your first cousin's son are second cousins to each other.
Your daughter and your first cousin's son are second cousins to each other.
Your sister's daughter and your son are first cousins to each other. Your sister's daughter and your son's daughter are first cousins, once removed to each other. Your son's daughter and your sister's granddaughter are second cousins to each other.
Your daughter and your sister's son are first cousins to each other. Your sister's son's daughter (her granddaughter) and your daughter are first cousins, once removed.
Your aunt's daughter is your first cousin, and her son is your first cousin, once removed.
Your niece's son and your daughter are first cousins, once removed.
Yes, you sister's daughter is your son's first cousin.