If you do not have a child custody and visitation order from the court with your soon to be ex wife over parenting rights for your son, you need to get one. In the petition for this order, you should mention your concerns about your son being around his aunt who is a smoker of marijuana and concerns upon the child's health as a result of being exposed to the marijuana smoke.Hopefully any child custody and visitation order issued by the judge concerning your divorce will take into account the possible dangers to his health if he is around his aunt, especially in a full time living situation.The above suggestion is the best way to protect you son's health.Good luck.