What is the proper salutation in a letter to a husband and wife with different last names?

Dear, Jim and Mary, Blah blah blah. Love, John and Carol On the envelope, you can address it to each of them by their full names each. Man or Woman first in the addressing is unimportant, just put whomever you are more familiar with first or stick with the man's name first. Another good rule of thumb is to write their names in alphabetical order. You can also stick to the method of how they sound together, for example, Francis and Xavier or Xavier and Francis.