Mr and Mrs its just more formal today in society.
Mr and Mrs
Mr and Mrs is correct or Mrs and Mr is correct
Mr. and Mrs. (ex. "Hello, Mr. and Mrs. Evans" instead of "Hello, Mrs. and Mr. Evans")
Mr. & Mrs. Smith
In the US it is normally Mr. and Mrs.
Dr. and Mrs. or Mr. and Dr.
I would address it to Mr and Mrs David Keys. For the salutation I would use Dear Mr and Mrs Keys.
"Mr" = "Herr". "Mrs" = "Fru".
It's Atty. and Mrs.
Well, my opinion is Mrs. and Mr. means their married. For example, Mrs. is married to a Mr..
It can be but Mr. and Mrs. Jones or Mr. and Mrs Carl Jones are equally acceptable.
Mr. Bill Mr. Pat Mr. Phil Mrs. Christine Mrs. Joanne Mrs. Evilyn