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