Dear Mrs Ambassador..
Rabbi and Mrs.
vmrs
Hello.
addressing attorney and wife
Dear Mr. John and Rev. Sally Smith,
Dr. and Mr. Smith.
Dr. and Mr. Smith
A letter would be addressed to Mr. and Doctor. If they are both Doctors it would be Doctor and Doctor.
You could address it to Reverend and Reverend Smith. The alternative would be the Reverends Smith.
"Dr and Mrs Smith" is the correct salutation. (With Smith replaced with the correct surname)
Dear Judge Smith and Mr. Smith.
probabaly just a mrs. would suffise