I really feel for you, but you do have to step out of the drama!! You seem to thrive on the chaos. Why do I say that? Well, you waste a lot of energy (and sanity!) by getting all wrapped up in the petty details. Let that boy's mom be a crazy loon if she wants to be. YOU have to choose to rise above that and do what's best for your stepson and the rest of your family. You'll do that by being focused, staying consistent with family rules and therapy, and just providing a loving home. I think you can do that!! You sound like you care and how great is that for that boy!!
For getting the legal stuff straight, be sure to write down everything that happens, all the times she misses appointments, visits, etc. That will help you get the story straight with the judge and hopefully get the right decisions made for your family. GOOD LUCK!!