politeness - How does one address a blended family in which the members have different surnames?

I am confused about how to address a family in which all the members have kept their original surname. What is the proper way to address such a family in a note to a family which consists of a single mother, her parents and children with 3 different surnames? For example, can one say, "Dear Smith family," even though that surname is not shared by the entire family?

Are hyphenated names related to this or is that only the last name of children born to parents who both keep their surname? If blended families do use hyphenated names such as Smith-Martin, is it possible for a family when the collective members have more than 2 surnames, to use more hyphens (e.g., the Smith-Martin-Jones family)?

I found this, which gives several options for writing an address from a blended family, but my question is about the interior of a card, not the mailing address, and the family is unknown to me except the names of the children.

Answer

On the outside, it's perfectly acceptable to address the envelope to the head of the family alone. For comparison, when you write to your bank, it's traditional to address the letter to "The Manager", even though he/she might not be the one acting on your correspondence. You could also put "Ms. Smith and family" on the envelope.

On the inside of the card is a different matter. You probably have more space to write; keeping things short is not as important. It's also potentially a more informal setting. (Unless you were sending a condolences card, which would usually be formal unless you were very close to them.)

In Australia, where I'm from, using the phrase "the Jones family" is very unusual as a form of address, though I gather it must be a more common usage in the USA. We usually address the inside of the card using given names (starting with the adults), e.g. "Dear Helen, Steven, Ben and Sarah". But then Australians these days use first names for business relations and even superiors, which might not be the case where you come from. It's also a common usage here to address the people you know by name, adding and family to include the others, e.g. "Dear Helen, Steven, and family" (in this example, Helen and Steven are the adults whilst Ben and Sarah are the children).

You say that the family is unknown to you, do you mean that they are all strangers? Or that you have met the mother but not the other family members?

Is there some social connection? For example, are the children connected to your own children through school, sport, etc.? In that case, you may want to list the children by their given names, rather than include them in "and family". Unlike children addressing adults, it's rarely wrong for an adult to address a child by their first name. It might look weird to write "Dear Ms. Smith, Bob, Ben, Amy, and family", you would have to judge whether you like that style.

If you have to stay formal, then "Dear Ms. Smith and family" might be your only option apart from "the Smith-Martin-Jones family".