If it is a formal letter, "Dr." or "Mrs." should be used.
In the body of the letter, Dear Doctor. On the envelope, Dr. Julius Banning [Ex ] .
Just as 'Doctor'
When addressing an envelope to the wife of a doctor who is not a doctor herself then and he is Dr. John Doe, then address the envelope to her as Mrs. John Doe or Ms. (Mrs.) Jane Doe.
If you're addressing it to both of them - It would be: Mr & Doctor Smith OR Mr & Mrs Smith - depending on how well you know them.
The address should read: Drs. John and Jane Doe or, Dr. John Doe and Dr. Jane Doe.
Dr. and Mrs.
Doctor Smith and his wife Reverend Smith (assuming she is using his last name).
You can address a retired colonel as "Colonel (Last Name)" and his wife as "Mrs. (Last Name)" or "Colonel (Last Name) and Mrs. (Last Name)" in the salutation of a letter.
Dr. Mary Smith and Mr. James Doe
Mr. and Dr. Joseph Smith (indicates the wife is the doctor)
To the wife only, just as Mrs. She has no title of her own.
"To Mr. and Dr. Smith." Or just separate the names, "To Mr. John Smith and Dr. Mary Smith." If it is a casual letter you could simply write "To The Smiths" I am guessing the original form of address you want to modify is "To Dr. and Mrs. John A Smith." But, this is an increasingly archaic form of address and is not applicable in the case of the wife being the doctor or professor nor can it be used when the wife has not taken her husband's name.
The best way to address your letter to a Minister is to Reverend and Mrs. _______
Govenor and Mrs. Beebe