Charles Challoner, ED559's bomb aimer, has unfortunately, not been easy to trace. However, I came across a match for a Pilot Officer CS Challoner on a memorial to members of the Manchester Police who died whilst on active service in the Second World War. I am assuming this is the same person as on ED559. Hopefully, this will provide an additional avenue for research.
UPDATE: I emailed the Greater Manchester Police Museum regarding Challoner and received some limited information confirming he was indeed a policeman before resigning to join the RAF.
He joined the police on 18 April 1934 aged 19 and it shows he was from Shrewsbury and was a Salesman. He married on the 21 April 1937. He resigned from the police service on 5 October, 1941 to join the RAF and his record card notes he was Killed in Action on 4 March 1943.