They're certainly not the first and only, even in Indonesia. The only fully-confirmed holder of bull shark in SEA was SeaWorld Ancol in Jakarta, apparently (Though not an official remark, this rumor was made by another user) an accidental catch, originally though to be one of their grey reef shark (Carcharhinus amblyrhynchos).
Again, we need picture of the sharks to verified that and if possible, all of them to see if perhaps one or two might be a genueine bull shark (Like SeaWorld does). I mean having not just one, but six "bull sharks" is both impresive and potentialy risky, for the other inhabitants and maintenance divers. How do you even know that they're mostly females to begin with?