Can crickets and mice be kept together?

No, keeping them in seperate terrariums is the best for both the mice and the crickets. As they both need different living conditions and their own space. Also I really hope you're only feeding the mice to the ball python and not to the bearded dragon, you can feed your dragon mice but only once in a while as they are very fattening. For the crickets I recommend feeding them "Fluker's Orange Cubes" or "Cricket Quencher". You shouln't leave very much water (if any)in your crickter terrarium as they aren't very bright and will often drown themselves. Just remember what you feed your crickets and mice is technically what you're feeding your ball python and your bearded dragon.

what's the difference?

they'll be exiting yure snake holding hands.