As for your correction. I wonder what's wrong with the original. I admit that there had to be "with" which I missed.
What context must correspond (with) each, so that they are correct?
(A dictionary example: Part of this report corresponds with the facts.) If a report can correspond with facts, I don't understand why context can't correspond with sentences.
(A book example by Eleanor Watts (she is British): Change the untrue sentences so that they are correct) I also don't understand why "so that they are correct" is not correct in my sentence.
As for the original issue.
Which one of them is you? - The subject is ONE.
Which one of them are you? - The subject is YOU
I don't understand how it is possible to have YOU as a subject in sentence 2.