Ive seen this before in divorces even without addiction some cough* parents (using the word lightly here)
Find it important that if they cannot bully the spouse or soon to be ex spouse then they push the kids to bully them. This is what it is much to our own recognition we know addicts use this tactic anyhow. So its no surprise really however I agree with others to inform your lawyer abput the conversation but
Dont be surprised if the judge asks your son to speak about the conversation which is usually the case.
I dont know what else you can do otherwise but try to be there when they talk.