Your son and your niece are first cousins.
Her daughter and your son are first cousins, once removed.
Your daughter and your niece are first cousins. Your daughter than your niece's son are first cousin's once removed. Your daughter's child and your niece's child are second cousins to each other.
Some nieces of sisters are related to each other and some are not. Your niece is the daughter of your brother or sister (your siblings). If you have more than two siblings and at least two of them have daughters, those daughters are your nieces and they are first cousins to each other. You can also have a niece who is the daughter of a sibling of your spouse. If two sisters have nieces who are daughters of their spouse's siblings, those nieces are not related to each other (unless the spouses are related to each other, as when two brothers marry two sisters)
Grand niece.
Your son and your niece are first cousins to each other. Your son and your niece's son are first cousins, once removed.
Your daughter's son is your grandson and you are his grandma or grandpa.
It does not appear that Thomas Jefferson had any nieces or nephews. He had a daughter, a son in law and two grandsons. He also had an aunt and a first cousin.
Your daughter and your niece are first cousins. Your daughter than your niece's son are first cousin's once removed. Your daughter's child and your niece's child are second cousins to each other.
The person is your nephew :)
your 5th cousin
They are second cousins
Amanda Perez has no children she has many nieces and nephews.
Your cousin's wife is not related to you or to your daughter - unless your daughter marries their son or your wife is related to your cousin's wife.