I don't see a problem with Nevill calling Jeremy (although I don't know if he did).
It's very difficult to work out the order in which things happened, but if Nevill did call him, it must have been before he was injured, and I would think before any shooting started. If there was shooting going on, I think he would have called the police or tried to get the gun off Sheila. He clearly didn't do that until he was attacked himself.