She may not love them, and telling the other two children that Mommy loves them.....could cause even more physiological problems about what love looks like. Maybe you should just stress how much you love them, but don't try to convince them that she does. Abuse is not love, and it sounds as if she's making them miserable when they are with her.
You are in a terrible situation, and it is outrageous for an adult to adopt children and then want to abandon them or send them back. Yes, Jim developed before our very eyes. Many of us were emotionally invested in his sitch. It took him a while to accept how cruel and selfish his W had become, but his strength came from God and his love for his five boys. He has his hands full, but the last we heard, he is happy and devoted to giving his best to his children.
If she doesn't want the other two children, and if they don't want to see her.....does the law enforce the visitation anyway?
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!