You would say "Dear Doctors" you wouldn't put the apostrophe.
Dear Doctors Jon and Michelle Smith
John Smith is the Doctors cover name. His real name is The Doctor, he chose it. If you were writing him a letter, I would say Dear Doctor.
My dear colleague
The salutation used for the envelope address can be either Dr. John Smith and Dr. Jane Smith, or Drs. John and Jane Smith. If you are writing a letter to both doctors, then he greeting in your letter can be Dear Drs. Smith.
dr Mary smith would be the correct way
To address multiple doctors, simply pluralize the abbreviation for doctor. For example, you would write "Dear Drs. John, Bob, and Sara".
Dear ms
it depends if you are writing a complaint it would be the title with out dear and if a friendly letter dear is correct
Drs. Joseph and Anna Smith number and street city, state, zip Dear Drs. Smith:
Dear Sirs and Madam:
Dear Father, Dear Reverend Father or Most Reverend Father
I BELIEVE THE CORRECT FORM WOULD BE: DEAR DR. AND MRS .....