You can't do that. You must sign just your own name (signatures do not, of course, include 'Mr' or 'Mrs'; you have to type or write the full name under the signature). The other partner must then sign separately.
Dr. Smith and Mr. Smith separately..
Yes.
Yes
The Honorable and Mrs. (first name with middle initial, if any) Smith
Dr. and Mrs. Smith
Dr. and Mr. Smith.
The Honorable Judge Smith and Mr. Smith for the envelope and Judge Smith and Mr Smith for the letter.
The proper way to address that letter would be "Mr. and Mrs. John Doe."
The Mouses. Since Mr and Mrs Mouse are proper names, they would not be contracted to a different spelling in the plural.
"Your Honor" or "Mr. (Mrs.) Mayor"
The name followed by Jr For example: John Doe Jr
Says the important that you want to say