Confused about the man they chase in the taxi and 'The Nightingale'

The man who they chase in the taxi and Ben kills in the factory is armed and appears to be hunting Ben/The Crew just as much as they're hunting him. He was armed, and could have escaped, but hunted them down and killed the first sound guy.

Later they're attacked in the hideout and the second sound guy is killed. Ben shoots into the ceiling and a man falls through. Ben then chases another man who he kills and explains that he is "The Nightingale". They also discover a film crew following The Nightingale and execute them.

Here's what I'm unclear on (because the film itself is not clear). They never mention or identify who the man who fell through the ceiling was. I'm not sure if he was part of The Nightingale's film crew or possibly The Nightingale's partner. Also, was The Nightingale there to kill Ben? It seemed as though he was. So was it more of a competition thing or was he hired to kill Ben? Also, the first man who they kill in the factory was also armed and seemed like he was after them, so was he also hired to kill Ben? It seems unlikely that he was just an armed civilian.

Obviously at the end we find out there are indeed people after Ben, the Nightingale's brother who has obvious Mob connections. But it's also possible there were more people throughout the film that were after him, or that there's a lot of competition between these killers and they're trying to take each other out.

Can anyone offer any insight into this?