When I was looking for “ye” in a dictionary, I stumbled upon the phrase “Who be ye?”. But why is it “Who be ye?” and not “Who are ye?”? The modern equivalent of “ye” would be “you”, wouldn’t it? “Who be you?” would be considered incorrect, whilst “Who are you?” would be perfectly fine.
There were several ways of conjugating to be in Early Modern English.
I am; thou art; he is; we are; ye are; they are;
I be; thou beest; he is; we be; ye be; they be.
I believe a combination of these was also used by some sources: namely, am/art/is in the singular and be in the plural.
"Who be ye?" is simply using the alternate form. But "Who are ye?" would have been grammatical as well, then, at least in some regions of England. Shakespeare generally used "Who are you?" and the King James Bible generally used "Who are ye?"
The OED mentions this in its discussion of Early Modern English grammar.
The “be” is subjunctive. Many uses of the subjunctive are dropping out of the language, but one still hears these constructions from time to time, and I confess: I love to use it in writing, even this “be.”
We still use “were” as the subjunctive quite a bit. Consider: “if I were you”...
Mostly we cue the subjunctive with an “if,” as in “if I were you,” but one can skip that “if” and say “were I you.” One of the most famous subjunctives in the English language starts Andrew Marvell’s “To His Coy Mistress”:
Had we world enough, and time, This coyness, Lady, were no crime
The word “had” in this example is also subjunctive. But all this sounds rather archaic because much of the special usages of the subjunctive mood have fallen out of common speech.