Messrs

An irregular plural: English never gave Mr an -s form of its own, so it borrowed the abbreviated plural of French Messieurs instead. It belongs to formal writing, such as letters, contracts and the names of firms. A single Messrs stands before the whole list of surnames: Messrs Hale and Carmichael, not Mr Hale and Mr Carmichael. The same spelling also serves as the plural of Monsieur.

Here the abbreviation is back in its home language, since Messieurs is literally the plural of Monsieur. That makes it the natural choice before French names, as in Messrs Rousseau and Bertrand. English uses one spelling for both titles, through the borrowing behind the plural of Mr. So nothing in the word itself tells the two apart. Only the names and the setting show whether the men are being addressed in the French style.