The lawyer should disallow it to preserve the attorney-client privilege. Otherwise, if he admits anything in front of you, it would be admissible in court. The attorney also has an obligation to his client only. If your son doesn't want to go to AA, the attorney has to fight against that.
And aside from that, I'd stay out of it. You know that being forced to go to AA won't do anything to help him get sober if he doesn't want it for himself.