Three together?
I knew this guy who kept 4 ball pythons in a 20 tall, I told him not to and that they needed more space. Well he didn't clean it out often enough and they ended up dying of respiratory problems. I've also heard of balls eating eachother, but that was just hearsay.
It' always recommended to keep them individually, they are not mice, they are not cats, snakes are loners, they only really meet up for breeding season.