Dear Messrs. [Last names}
Dear Mr. President is a salutation of a business letter. The salutation goes at the beginning, thus that's how you got Dear.
Traditionally, Mr and Mrs (insert last name). She took his name in marriage.
I would address it to Mr and Mrs David Keys. For the salutation I would use Dear Mr and Mrs Keys.
Master
Mr. John Jones.
Mr. Mayor
Mr. President
Mr. Commissioner
In the salutation line of a letter addressing multiple men and women, you can use "Dear All" or "Dear Team" for a neutral and inclusive approach. If you prefer to be more formal, you can list the recipients, such as "Dear Mr. Smith and Ms. Johnson," or simply "Dear Mr. Smith, Ms. Johnson, and Team." If there are many recipients, "Dear Colleagues" can also be appropriate.
The salutation of a letter addressed to two men named Smith is:Dear Messrs. Smith,The plural of Mr. is Messrs. from the abbreviation of French messieurs (which is the plural of monsieur).
The proper salutation for a psychologist is "Dr." if they hold a doctoral degree (PhD or PsyD) or "Mr." or "Ms." if they do not have a doctoral degree. It is always best to refer to them based on their level of education and preference.
Dr. and Mr. Smith.