I feel sad for the children but, feel for Jane most, Dee. In situations such as these, we must treat the cause before the symptoms unless, of course, the situation poses imminent threat to the children i.e. sexual or physical abuse, where urgent action for social intervention becomes necessary. From what Amy has confided in you, the children and their mother are suffering as a result of an unhappy marriage. Jane's addiction to pills is perhaps the manifestation of that unhappiness. The rest are "consequentials".

Sometimes, the saving grace in circumstances like Jane's is a friend. You may be that friend, Dee. Your friendship may not change her marital situation, which seems to be a significant part of her problem, but, it might make a big difference to her. The children are fortunate to have found you and perhaps, they're the conduit which leads to help for Jane. The fair would be a good excuse to spend time with her and the children. It could be a starting point of that friendship and at the same time, Judy would not feel bad about her Mom not taking her.