questions - "Who is speaking with each other?" Is this correct?

When who and what are used to ask for the subject of a clause, they most often have singular verbs, even if the question expects a plural answer.

Practical English Usage, Michael Swan, Third edition, Page 525

So we say:

A: Who is speaking?
Q: John and David are speaking.

How about this one? Is it correct to ask:

A: Who is speaking with each other?

For this answer:

Q: John and David are speaking with each other.