Well said OldChina, so much libertarian tosh has been spouted here.
If I was head of security for an airline and I was advised that I had a pilot working in the airline who had a brother and a friend in an extremist Muslim organisation that had two members, known to the pilot, who were seeking to learn to fly at the rate of four lessons a day I would smell a rat. Imagine, one already on the flight deck as legitimate crew, (negating cockpit door security), with two accomplices in the cabin ready to pounce on a given signal and all three hell bent on suicide.
It is possible that insurance underwriters came to learn of this situation and they may have discussed withholding insurance cover, who knows?
Pay the man off, the circumstantial evidence seems to suggest he was an unacceptable risk.