FAQ for
The Edge (1997) More at IMDbPro »

An interesting question, the most likely answer is no. He wouldn't have anything to gain from killing Charles, unless Bob was going to pay him. But given that the movie never really suggests that Stephen was in on the plan, such as; When Charles asks Bob on the plane how he planned to kill him, it would be wise for the camera to show a shot of Stephen with a look of suprise or fear as if the plan had been discovered. This doesn't happen. Also when Stephen is laying by the fire he tells Charles that he thinks highly of him and appreciates all Charles is doing for him. The film basically has him as an out-of-the-loop character along for the ride. Later on in the film when Bob says he couldn't kill Charles while Stephen was there because Steve is the only one who knows how Bob likes his coffee. Stephen responds as if they were all joking around, so he was ignorant to the fact.

The only real evidence supporting the fact that Stephen MIGHT have been in on the plan was the tagline for the film "Three men were fighting over a woman when they crashed....." But that is just a tagline, to quickly sum what the film is about. Instead of saying "two men were fighting over a woman and a third guy that was with them wasn't listening to the conversation when they crashed..."