Firstly I am sorry that this happened to you and your son. I can't imagine what you went through. I have hunted with my son nearly every weekend of the season for the last four years and I can't imagine what I would have done had this happened to me.
I think that I would do the following:
I would be inclined to kick the crap out of him on the spot, (if I thought I coiuld) but since your son and his are involved I wouldn't do that in front of them.
I would immediately call everyone else in the club and tell them what happened and move to immediately suspend this guy from the club and never let him back, even if you have to refund a prorated portion of his dues.
In my state it is illegal tol hunt game from a moving vehicle and aalso illegeal to discharge a firearm from a public road. IF the same applies to your state I would swear out a warrant with the Sherrif and have his butt served and forced to appear in court where you can tell the judge what happend and he would then be forced to explain himself. Revocation of his hunting icense would be one of many possible outcomes, and that should happen. This guy is too reckless and stupid to have the right to hunt.