1. The city was the detention camp as the number of people was so large, once they're inside they almost just have to fend for themselves. The gun battles/uprising only seemed to start that morning, because the Fish blew their way into the camp to get to the girl.
2. Like many groups, there are different factions, they all wanted the same thing but some of them had some really bad ideas about how to do it.
3. Probably more out of shock than anything, seeing a "miracle" like that would probably make most people not realise what they're supposed to do.