Technically, Messrs English, although it would be more polite to call them Mr Fred English and Mr Joe English if their given names are known.
"Mr. President" is the proper address for the US President. "Mr. Obama" would probably not offend him.
Mr. President.
Generally, Mr. Reddy would be considered the proper way to address someone. However, in the South, Mr. Santosh would also be acceptable, depending on how well one knows him.
Mr. and Mrs. John Smith III
You would write it as: Mr. John Smith c/o, (address)
The proper way to address that letter would be "Mr. and Mrs. John Doe."
I would address it to Mr and Mrs David Keys. For the salutation I would use Dear Mr and Mrs Keys.
yo dude
You would address them as Mr.and Mrs.Smith
In speech, Mr. Hoffman would be called Herr Hoffman. In writing, Dear Mr. Hoffman, would be Sehr geehrter Herr Hoffman,.
MESSERS
No, that is not correct English. The correct English would be:- "Please add Mr. Mark to tomorrow's session".