Given that "kiabálnak" is in 3rd person pl, would this theoretically be more accurately translated as "Who are they that are shouting in front of the store?"
That's true. The original sentence does carry more information than the translation though, which is the number of "people I'm hearing", so to say. There isn't really a way to properly translate that to English (without losing accuracy otherwise, like with my suggested translation) though, is it?
Well, right, strictly doing it, this information will be lost in translation. But if it is important to convey the plural, then there are ways. For example, the way you wrote in your sentence. We have to make those people a specific group. Another solution:
"There are people in front of the store, shouting. Who are they?"
Just for your interest- you might well know this anyway- that in the north-east of England (Newcastle, Durham, etc) you have a plural form of you- "yous" which is used, and which people not from the area may occasionally use to make the distinction between singular and plural- (but it would be informal). I imagine that elsewhere you don't normally have that because the context usually makes it clear or the distinction unnecessary.
Another kind of translation that changes it but gives the idea more naturally could be: "Who are those guys shouting over there?"
"Who is shouting in front of the store?" = "Ki kiabál az üzlet előtt?"
"Who are shouting in front of the store?" = "Kik kiabálnak az üzlet előtt?"
No - English takes the single verb form after "who" unless there is a explicit plural noun.
The plural form is still not accepted on 07th of January, 2018. Reported.
When using "who" to ask for the subject, the verb needs to be in 3rd person singular. -"Who is shouting?" -"They are." -"Who knows the answer?" -"We do."