AA is a program of recovery for the alcoholic, and I myself as well as many others on this board attend meetings and work that program.
Alanon, on the other hand, is a program for friends and family of alcoholics. It would be you and those close to your son who wish to help him that would be going to the meetings. The entire intent is to enable you to help your son in the way that has been found to be the most effective through years of experience.