I think the word's alright. Except plenty of people say "all y'all", so it doesn't quite fulfil the function as the English "vous"
No, when I hear y'all its usually coming out of a persons mouth who lives in texas or something, wears dungarees, drives an old battered pick up truck, owns a shot gun and a banjo.
(Stereotypically speaking of course, just to prove my point)
I've never heard it said here in England on a regular basis, and if I do I'll find the nearest cliff and jump off it. lol, You's or you all will do.
tbh i would probably either say You all or more likely All of you.