In the United States, more than half of all marriages end in divorce, and 68 percent of men and 78 percent of women remarry, according to the National Center for Marriage Family Research. This often leads to a family sharing several last names. Other couples marry and keep their original last names, for personal or professional reasons. When a family includes more than one last name, the etiquette for addressing envelopes to them is a bit different than a family with only one last name.
The Basics
List either the husband or the wife first, according to EmilyPost.com. You could write: Ms. Joan Clark and Mr. John Rich or Mr. John Rich and Ms. Joan Clark. It's also acceptable to write the name of the person you feel closest to first. If one has a professional degree, then list that spouse first. If they both have a professional degree of equal rank, then list the spouse whose first name is first alphabetically. According to The Knot, for same-sex couples, you'd arrange the names the same way you would for any other couple. For example, you might write: Ms. Ann Smith and Ms. Julie Bond or Mr. James Williams and Mr. Steven Roberts. If a couple is unmarried, you'd list their names on separate lines.
Children Have Different Last Names
For a remarriage in which the children are from the mother’s previous marriage, girls under 18 have a title of Miss and boys don't use a title until they're 18, when they use Mister, according to The Knot. If you're addressing an invitation, you'd only include their names on the inner envelope. On the inner envelope, you might write: Ms. Ann Smith and Mr. John Smith, Billy Jones and Miss Emily Jones.