I am trying to talk with the courser to start the quest, but every time the brotherhood comes and starts attacking, and he runs off and attacks them so I can't finish talking to him to start it. I can't attack either of them, and he doesn't die, while they don't die either, just sits on the floor after he's hurt since he's a quest person.

I just killed the brotherhood guys. Then you can talk to him.

Thanks, I will try that. I shot at them a couple times but didn't know if it was possible for them to die, because they didn't have a health bar show up when I did it since I am allied with them.