In this type of game, the player often has to switch back to the character he or she was controlling immediately before, but the amount of operation required is high because the switching is one-way.
In addition, when the controlled character goes off-screen, the player's recognition load increases considerably.
All of this adds up to more time spent just manipulating puzzles than worrying about how to solve them, and that's a shame.
I think it would be more intuitive to use two keys to switch between characters in both directions, and base the switching on the character's X coordinate.
Also, since the entire level is large and involves a lot of movement, it might be nice to have a mode where you control everyone at the same time. Or perhaps we should simply shorten the distance we have to travel.
Anyway, it was a well-made and fun game.