They bite and the other flips around every which way like many animals do when trying to escape an attacker so it twisted the tail like that. And cutting does no harm, the harm is already done, the tail cannot heal + the other dragons will probably bite it again. But I'm not going to pressure anyone to do what they are not comfortable doing. So did you get these from a store + they convinced you to take 3 ?
Just feed these guys like crazy, 3-4 X a day so they are not tempted to bite more. Even then it's a good chance of happening again. Keep bowls of greens in the tank as well.