"Who are" vs "who is" [duplicate]

Sentence: it's not what's on the table that matters, but who (is/are) in the chairs.

I thought are might be correct because of plural chairs, but family members disagree.

Related: https://ell.stackexchange.com/questions/22900/who-singular-or-plural

Closed, nearly-identical question (off-topic): Can "who" be plural when it is the subject of a sentence?

Relevant discussion: http://thegrammarexchange.infopop.cc/eve/forums/a/tpc/f/340600179/m/7756074182

Who can be both singular or plural dependent on the noun which it is replacing. 'Chairs' in the plural implies that some sentient plural noun will be occupying those chairs.

'Who is' in the chairs would imply a single entity occupying multiple chairs. 'Why are you in my chairs?!' An interesting thought.

'Who are in the chairs?' correctly identifies the chairs' occupants as plural and thus is the correct format.

[no longer relevant to original question]

The matter seems to be discussed. Some sources indicate that interrogative form of who is always singular (end of first paragraph: “Interrogative pronouns are never plural”).

Who is in the chairs?

Who does the being, it is subject, therefore the verb is singular person.

Now, it might be acceptable to use a plural in some edge cases. In A Comprehensive Grammar of the English Language (1985 Quirk et al.), page 756:

Similarly, interrogative who and what as subjects normally take a singular verb even when the speaker has reason to believe that more than one person or entity is involved. However, a plural verb may be used if other words in the sentence indicate that a plural subject is expected in the answer

It is still inadvisable though. For instance, on page 371 of the same book, it says that

even though several voices are heard outside, the natural question will be Who's there? rather than ?*Who're there?

The ?* sign is used in the book for marking mostly yet not completely unacceptable examples.