"chers messieurs, "
It is not recommended that a writer use "Dear Gentlemen's" in a salutation. "Dear gentlemen's" is referring to the gentlemen's object, not the men themselves. Try using "Dear gentlemen" instead.
I would recommend Ladies and Gentlemen.
The phrase "dear gentlemen" is grammatically correct, but it may sound a bit formal and old-fashioned. It is more common to address a group of people as "gentlemen" or "dear friends" instead.
'votre Cher roi'
The salutation is a from of greeting: Dear Mr. Smith: Dear Ms. Brown: Dear Professor Green: Dear Doctor Jones: Dear Professor Green and Ms. Brown: Dear Doctors Jones and Jacob: Dear Sir: Dear Madam: Dear Sir/Madam: Gentlemen: Ladies: Gentlemen and Ladies: To Whom It May Concern:
Cher Monsieur is Dear Sir. if you know his name is Dupont, write Cher M. Dupont
It seems only if your familiar, as 'dear' is a familiar term.
Welcome to the party, ladies and gentlemen.
"messieurs"
messieurs
Dear daughter is 'chère fille' in French.
Singular ; Sir. Plural ; Sirs. However this is rather awkward. More correctly it is 'Messrs.' ( pronounced 'messers'), If writing an epistle (letter) to a man, you write , 'Dear Sir', However if the letter is to a group of men you write 'Messrs,' (NOT dear messrs.) If speaking to a man , then it is 'Sir'. However, if speaking to a group of men, then it is 'Gentlemen'.