Covemonty 1 acts before 2, who acts before 3 etc, and only once all 4 have acted (or done nothing) the water is checked for. This means that if Covemonty 2 turns into a pushable block and on the next turn Covemonty 1 pushes 2 onto water, 2 will have time to perform a move before sinking as long as the move takes it out of the water.