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.
There is no character named Mr. Guareschi in the book "Wednesday Wars" by Gary D. Schmidt. The story focuses on Holling Hoodhood, a seventh grader living in New York during the late 1960s.
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. used to be acceptable to address a household by just using the last name, e.g. "Mr. Jones". In modern times, it is typically to use "Mr. and Mrs. Jones" or "Mr. and Mrs. Timothy Jones".
Mr and Mrs its just more formal today in society.
"Mr" = "Herr". "Mrs" = "Fru".
It can be but Mr. and Mrs. Jones or Mr. and Mrs Carl Jones are equally acceptable.