The way you posted the question, at first I thought you were talking about Six. It just occurred to me that you might not realize that the term ghost was a metaphor. Just like the CIA, KGB, and other secret acronym holders are called spooks.
The ghosts are not really dead. All of the ghosts deaths were faked so that the ghosts could pursue dangerous people without repercussions to the ghosts’ families. Their “deaths” frees them from ties of responsibility and paper trails. They no longer have anything to lose and nothing that can be used against them.
In the opening dialogue, One is doing aerial stunts and aerobatics above a lake, river or gorge. He performs an intentional tail slide, and bails out. You then see him outside of the plane with a pilot-chute (the small canopy that pulls the big canopy out) above him. Any wreckage found in the lake/river without a body would be consistent with a high angle impact with the water.