Mrs, Mrs & Mrs
"Dr and Mrs Smith" is the correct salutation. (With Smith replaced with the correct surname)
Yes.
Rabbi and Mrs.
Dear Mrs Ambassador..
Dear Mrs. Obama,
Dr. and Mr. Smith.
probabaly just a mrs. would suffise
"Your Honor" or "Mr. (Mrs.) Mayor"
Dr. Smith and Mr. Smith separately..
Mr and Mrs would be proper. Attorneys are typical written to as Mister.
Mr for males and Miss, Ms or Mrs for a female.
Mrs Smith, unless she has specifically changed her surname back to her maiden name