the only times i have seen my cresteds biting eachother were:

1. i had 4 juvies together. i witnessed one of them biting the another and separated the one that was getting bitten. it soon turned out to be male. the same thing happened with one of the other juvies a few weeks later.

2. i put a new adult female into an enclosure with 2 other adult females. one of the females nipped twice at the new one and they then commenced to all get along perfectly. i guess it was just a little initiation/i'm checking you out kind of thing.

in any case it may be best to separate them until you see what sex they are. if both females they may be able to be reintroduced with supervision to make sure they are getting along ok.