Complex sentence: She and Bill, the only two left alive and unaware of what's going on, leaves the main cabin to investigate and to discovers a bloody axe in Brenda's bed and that the phone lines are dead and the cars are unable to start.
Split into simpler sentences: She and Bill, the only two left alive and unaware of what's going on, leave the main cabin to investigate only to discover a bloody axe in Brenda's bed. The two also discover that the phone lines are dead and their cars are unable to start.