Why is "Mine" included?
It's part of the set phrase. "My ladies and gentlemen" is how it's expressed in Norwegian.
Same in french "Mesdames et Messieurs" ( comes from : Mes dames et mes sieurs) :)
Herrer means both lord and lords?
Herre is singular, herrer is plural.
Velkommen til Norge!
Is it vital to include "mine"? I hardly ever hear "MY ladies and gentlemen..." Usually just "ladies and gentlemen..."