Your daughter's daughter is your grand daughter.
Your nephew's daughter is the granddaughter of your sibling (your brother or sister)
The grandchildren of siblings are second cousins.
Second cousins once removed.
Nieces are the daughters of your brothers and sisters. Nephews are the sons of your brothers and sisters.
They are your grand-nephews and grand-nieces or great-nephews and great-nieces.
Your niece and your daughter are first cousins. Your daughter and the daughter of your niece are first Cousins, once removed.
Your daughter's daughter is your grand daughter. Your nephew's daughter is the granddaughter of your sibling (your brother or sister) The grandchildren of siblings are second cousins.
Your brother's sons are called your nephews, and his daughters are called your nieces. Collectively, you can refer to them as your nieces and nephews. If you want to be more specific, you can say "my brother's children" as a general term.
They are second cousins
Your daughter and your nephew are first cousins. His daughter is your daughter's first cousin, once removed.
Tiffany is her only daughter. She also looks after Whitney, but they are not related.
They would be great nieces or great nephews.
Absolutely not-- Joan has said countless times that she wishes she had a daughter...... that she has many "adopted" daughters. but NO daughters---- real or adopted.
You should write daughter's if you are talking about one daughter, e.g. "it is my daughter's birthday tomorrow".You should write daughters' if you are talking about more than one daughter at the same time, e.g. "this is our daughters' bedroom, which they share".