It depends on society's view of the creatures, their control over their wereishness, and how much the higher-ups know about each other.
Assuming the most likely situation, that society fears and hates them, that they totally lose it once a month, and they they more-or-less all know they are all werewolves, it become simply a game of self-preservation and MAD.
Threats:
Losing control over yourself once a month, even if it's by turning in a fearsome beast, is a very vulnerable situation for somebody with lots of enemies, both within your organization and without. Seriously, it just takes ten guys armed with silver weapons.
Gangs, while always hated by everybody, normally operate more-or-less under-the-radar, and rarely are outright despised by the whole of society. If word gets out that the capital city is run by monsters hated by everybody, no matter how strong they are, they are eventually going to fall to the force of an enraged public.
Therefore, you'd have to keep this knowledge as concealed as possible from everybody, probably by threat of personal harm. It's easier if they have something to gain from you on a regular basis, so gang leaders would have to keep both whichever of their members and their 'property' who discover their secret convinced that it's in their best interest not to spill the beans and bring it all down. Of course, if they get too greedy, well, dead men don't talk.
MAD:
The reason mutual assured destruction would set in is because the leaders of each gang know all the above. While they may try to kill and destroy each other, a stability would develop simply because they have an unstoppable weapon: knowledge that the other gang is full of wereanimals. Move too far or push too hard, and eventually somebody will drop the bomb, even if it destroys them as well.
Given the assumptions made at the top, there's no reason they'd ever want the word out, no matter how much the personal threat could help them. The information is just too dangerous.
