Not a duplicate of, but inspired by: A position in which checkmate is forced (obligatory)
That question has a bit of variation, and my question is far more specific.
My answer to it was like this:
[FEN "RN2k1NR/P3P2P/3PPP2/4pBp1/4PbP1/3ppp2/p3p2p/rn2K1nr w - - 0 1"]
This is a position in which all possible moves, the only moves possible, are checkmates. They are forced in the sense that they are the only options. Their are 14 possible mating moves combined, and 10 mating pieces/pawns total (the rook mates are attirubuted to the knights.)
This position is clearly illegal, so I wonder what legal position, legally reachable, has the most possible forced checkmates is within the already given criteria.
Whether one side or both are used matters not: In the end the TOTAL amount of possible forced checkmates is what matters.
Their are two categories for this I suppose: Most moves and most pieces and pawns.