"You all are from Europe."
Translation:Ihr kommt aus Europa.
There were no brackets or "alle" in my original answer, just "Ihr seid aus Europe." Sorry for the confusion.
I think the "all" in the original sentence was just to indicate that it was a plural form of "you", but since the german form includes the "pluralness" it is unnecessary to put "alle" in the sentence again.
Except that most of us don't say you-all as a plural for you. So "Ihr kommt alle aus Europa", and "Sie kommen alle aus Europa" should both be marked as correct. Unfortunately, I was on the timed test for this and got interrupted in the midst of doing it, so missed my chance to report; did it a second time, but didn't get this particular sentence to translate. So basically, I'm just hear to complain!
If you don't give us social clues about the status of the audience, then DON'T mark us down for differing between Sie-Sprache and Du Sprache!
I am unclear as to why this plural subject uses the verb kommt instead of kommen? If it was they, would it be kommen?
That's just what the second-person plural form of the verb is: kommt. The second-person plural is always(?) different from the first- or third-person plural verb forms.
It depends on whether you understand it as the second person, ihr (Ihr) kommt, used to address children or good friends, whom you would address by du (Du if friendly but still polite) in the singular, or as a group of normal people, in which case you would use sie kommen (they come), or as a formal, polite addressing of a single person, in which case you would use Sie kommen (meaning you come, but using the plural form to be formal and polite), which has to be written with upper case S.