Very interesting!
I think it stops going through the door, even with both of them at the exit at a certain level (which was pretty hard, actually), and it doesn't go any further. For now I assume that may be on purpose.
You did a really great job on this! I actually think this may be a bit on the challenging side actually. The mechanics worked very cleanly!
To make it easier for some players, perhaps an easy mode where if they cleared with one character, they don't have to repeat that character too if they fail with the other one, as it can be hard enough even with just clearing one for many players.