Fun concept! it felt fun to control multiple character but there's no real incentive to. The optimal way of completing each level is to have 1 maybe 2 characters (so you have a backup in case one dies). Then moving very carefully through each level taking the safest path.
It's okay to make your player have to engage with the most fun part of the game or else your game is just incentivising them not to play with it, thus making it boring.