When your letter is to more than one person, write out all of their names separately, separating them with commas. For example, "Dear Mr. Hobbes, Ms. Luxe, and Mr. Hopman." For married couples, if one person in the couple has changed his or her name, you only need to use the last name once. For instance, "Dear Mr. and Mrs. Smith."
Parts of Business Letter. A business letter will be more impressive if proper attention is given to each and every part of the business letter. There are 12 Parts of Business Letter. The Heading or Letterhead,Date, Reference, The Inside Address, Subject, Greeting, Body Paragraphs, Complimentary Close, Signature and Writer’s Identification, Enclosures , Copy Circulation, PostScript