Mr and Mrs would be proper. Attorneys are typical written to as Mister.
addressing attorney and wife
Depends on whether you wish to be kind, or offensive, right?
Dear Mr. John and Rev. Sally Smith,
The Honorable (similar to a judge)
You could address it to Reverend and Reverend Smith. The alternative would be the Reverends Smith.
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.