In the world of business and academics, there is etiquette to follow and rules to live by. While addressing a group of doctors, the "wrong" way won't result in your letter in the trash, but it's certainly not going to earn you any bonus points. When writing a letter to multiple doctors, you must address each doctor on the envelope and inside the letter. You also should address married doctors differently than unmarried doctors.
Begin by addressing the doctors on the envelope. Write each doctor's full name, with "Dr." before the first name, regardless if the doctors are married or not. For example, for Doctor Jason Smith and Doctor Jane Plum, address them as "Dr. Jason Smith and Dr. Jane Plum."
Address married doctors -- two doctors who are married to each other -- inside the letter starting with "Dear Doctors." Write the first name of either the man or woman, followed by the first name of the remaining spouse and then the couple's last name. For example, to address Doctor Bill Ham and Doctor Jill Ham, write "Dear Doctors Bill and Jill Ham."
Address multiple doctors -- who are not married to each other -- by beginning with "Dear." Write "Dr.," followed by each doctor's first and last name. A "Dr." should precede each doctor's name. For example, if you were addressing Doctor Jack Gill, Doctor Suzy Till and Doctor Timothy Mint, you would write "Dear Dr. Jack Gill, Dr. Suzy Till and Dr. Timothy Mint."