Dear Mr. John and Rev. Sally Smith,
You could address it to Reverend and Reverend Smith. The alternative would be the Reverends Smith.
Rev. when in written form. Reverend in spoken form.
Mr and Mrs would be proper. Attorneys are typical written to as Mister.
This could be done in several ways. I believe the current best practice would be The Reverend and Mr. Smith.
What is the proper etiquette to addressing a Reverend in a letter?
Assuming a business letter to husband and wife with different last names who you don't know the proper business salutation is to have the the wife's name first before the husband's accompanied by the proper titles. For example: Dear Mrs. Thompson and Mr. Jones, (salutation on letter) Mrs. Susan Thompson and Mr. Jeremy Jones (address on envelope and letter) Note that you could use "Ms." instead of "Mrs." if you prefer, although I recommend that since in this example you know they are married I would choose "Mrs." Jim Lumley jimlumley@live.com
Dr. and Mr. Smith
To whom it may concern
Rabbi and Mrs.
Dear Counselors:
A proper salutation for greeting the president of a business is "Dear Mr. President". To conclude a letter, the proper word is "Sincerely" and a the name of the writer.
"Dear" is what people use it nowadays.