I would be grateful she isn't ignoring them or abusing them and be thankful that your children are loved enough to have multiple people who want to take care of them. This isn't about you. It's about your children and how they will eventually grow into adults and have formed opinions about divorce and parenthood. Put yourself in her position. If you were a step-mom and your step-son was at your house for the weekend, wouldn't you want to care for him while he was there? If that means inspecting his teeth before bed or putting soap in his mouth because he said an inappropriate word, wouldn't you want the "real" mom complaining about you because of that more than her complaining that you ignored the child and didn't speak to him the whole weekend? Seriously. If you are a good mom, your kids will see that. They will also see your insecurities if you constantly worry about her "over-momming" you. The best way to get over on someone if you think they are doing something on purpose to hurt you, is to acknowledge it and tell them how grateful you are that she is taking as much investment into your children as you are and how important it is to you, for your children to grow emotionally healthy through all this grown-up drama that isn't their fault.
**Can I just say...after I wrote this, I scrolled through everyone else's comments and for the most part I think most of you are completely off base. First of all, get over the whole SOAP thing. It's soap, people. It's not rat poison. Some of you talked about going back to court, being upset at the dad, and it being wrong for the step-mom to have contact with the kids' school. ARE YOU SERIOUS? Illegal for this woman to be involved in the upbringing of children belonging to people that didn't set a good example in the first place? Unbelievable for women to give another woman the advice you gave her. You want her to set boundaries on how much love she can show those children. If she would have written a post stating the step-mom was locking them in closets, not cooking them dinner, calling them ugly names, THEN give her the advice you did. Don't keep the vicious circle going by encouraging her to keep broken bridges instead of working together.
M., I'm sorry if I made you mad. I don't know you and don't have anger issues. But what I do have is a huge desire to retrain our children from being raised thinking everyone divorces. Right now, your children AND my children have a much higher probability of divorcing when they are adults because they are growing up in a divorced home. If you can turn this situation into the most positive experience you can, (I realize you can only control yourself) and show your kids that divorce can be positive, then and only then, do you have a shot at them growing up to be secure adults who choose their mates wisely.