The guy in hospital is really Cameron. The one who everyone thinks is Cameron is really Robert. The real Cameron is the nice one, real Robert is the nasty bloke that's bumping everyone off. He has an axe to grind with his Dad and is systematically destroying him by getting at the people he loves.
Now, the one in hospital, the real, nice Cameron, is there because of a car crash deliberately caused by the real Robert. Everyone thought he (as Robert) is missing.
Got it so far?
The nun-girl is Carmella, an ex-girlfriend of Irish Connor. She told Connor that she'd seen a guy like Cameron/Robert in her hospital. He investigated and then told Robert (who he thought was Cameron) that his brother had been found.
This is a problem for real Robert, and we think he's now bumped off Connor to stop him telling everyone else.
Does that help?