If the couple is not married, address each person with the appropriate title. Write each name on a separate line, as you would for an unmarried opposite-sex couple. The order of the names usually doesn't matter, but if you're unsure, arrange them alphabetically. If the couple is married, you should write both names on the same line, separating them with "and." You can choose to give each name its own title like Mr. Alan Johns and Mr. Dan Evans. In most cases, same-sex couples will keep their last names after marriage. You may want to consider ordering the names alphabetically.