I'm filling an English document and I'm being asked to complete my family name, then my name at birth and then my first names. Does anyone know the difference between these 3 concepts? My guess is that my family name is my last name, my name at birth is my complete name at birth, and my first names are everything but my surname. Is that correct?
Here's the common usage of those terms but for a specific form check with whoever is asking for the form to be filled out.
Family name is the part of the name you share with your family, often called "last name" or "surname" in English (though that's less accurate since some cultures put the family name first).
Name at birth would be your full-name on your birth certificate (usually the same unless you've changed your name).
First Name is your given name (strange to see a form that mixes "first name" and "family name") if it says first names (plural) it might include all other names other than your family name (eg middle names).
They are attempting (poorly in my opinion) to come up with a way of getting full accurate name information that would apply cross culturally. In some cultures, the concept of "first name" is different than other cultures, especially those where the family name is said first, FOLLOWED by the given name. In some religions, you have a "birth name" but also a "Christian name" given to you at Baptism or Confirmation. Different again is the fact that some families will have official "first names" on the birth certificates, but everyone inside of the family uses what others would consider "middle" names. My wife's family from South Dakota was like that; her mother's name was Virginia, but everyone in the family called her Fay. Her aunt's name was Nancy, but everyone called her Ruth. In both cases those were their middle names. Confused the heck out of me until my wife explained it.