I disagree, (An Urdu speaker here learning Hindi script). The sentence is correct.. ve kaun haiN . haiN हैं denotes plural and you need not add lohg in the sentence at all. lohg is an altogether different word and you sentence ve log kaun haiN would mean who are those people. lohg means people.
I'm confused, Duolingo accepted "Who are they" for both "ये कौन हैं" and "वे कौन हैं".... Is there a difference? Ziyan819860 mentioned that he doesnt believe the sentence makes sense at all, and this really disappoints me as I want to be understood when I'm India and not make a fool of myself :-(
As I wrote above, I am pasting it here
There is a big difference between ये (this) and वे (that) . "ये कौन हैं" Who are these? ये is used for both this, it, these. वे कौन हैं" Who are those? वे is used for that and those.
Please refer to my answer to Ziyan819860 about his comment