Denise and Paul Jonas' (their parents) anniversary is August 15th, which is also Joe Jonas' birthday.
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")
Not necessarily. Just Mr. & Mrs. as you would address any couple. Relatives name only for Birthday cards. Christmas , Anniversary , any invitations for both should be Mr. & Mrs.
Mr. & Mrs. Smith
In the US it is normally Mr. and Mrs.
The cast of Their First Anniversary - 1914 includes: Max Asher as Mr. Younghubby - the Husband Louise Fazenda as Mrs. Younghubby - the Wife Billy Franey Bobby Vernon
Dr. and Mrs. or Mr. and Dr.
For the 50th Wedding Anniversary invitation the man's name comes first: Mr. John Doe and Mrs. Jane Doe or if it is not that formal it could be 'John and Jane Doe.'
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.