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".
I don't think it really matters. But in society today you normally say Mr. then Mrs. I would do that to be safe.
Mr. and Mrs. (ex. "Hello, Mr. and Mrs. Evans" instead of "Hello, Mrs. and Mr. Evans")
Mr and Mrs its just more formal today in society.
In the US it is normally Mr. and Mrs.