Simul in which the GM has to make identical moves Consider two simultaneous matches in which a GM plays against Players A and B, constrained by the rule that the GM must make identical board moves in both games. Players A and B can play as usual.

Thus, for example, if Player A takes one of the GM's pawns, but Player B does not, then the GM forever loses the ability to move that pawn on Player B's board as well.

The GM only wins by winning against both Players. We can also stipulate two versions, in one of which Players A and B can cooperate, and in the other of which they cannot.

Question: Could two average Players A and B always win against the GM in this setup? Would it matter if they are allowed to cooperate or not?

(I'm not necessarily looking for a mathematical demonstration of the answer, though if there is a simple winning strategy, that would be nice. I would be glad to hear from good players about what they think would happen.)
If I understand your proposal, I think that the constraint that you are imposing would make it too easy to defeat the poor GM. Let's imagine the following pair of games with the GM playing Black:

1. e4 e5
2. Qh5 Nf6
3. Qxf7#

1. e4 e5
2. Qf3 Nf6
3. a3


Qxf7 on the first game is "checkmate" because even though Black would simply capture the queen in a normal game, they can't do it here because they can't make the same move on the second board.