Could plural "you" be written, "You all"?
Yes, a lot of other problems accept "you all" or "y'all", so this is just an error that needs reporting.
You all are rather than You are all is Southern English - y'all and all y'all. :)
You all are and You are all buying shoes is the same thing!
Is it? I actually don't know
in english, both "you all are buying shoes" and "you are all buying shoes" are correct but i think "you are all..." is more idiomatic. it may be a dialectical northern vs southern USA difference though