I was just reading your thread and my heart goes out to you. I would say you are doing a great job with both your children and I am sorry your W doesn't see it.
In reading all the stories of your W..I don't know too much, but I had a friend who went through something very similar with his wife. His W would act out aggressively and say things, then not remember (the way you said she didn't remember hitting and kicking you). It turned out she had bi-polar disorder. When she finally got help it was a huge difference. But she would litterally snap at everything he said even when he was calm as could be.
I don't know too much about your wife and I am not a doctor. It also sounds as if she may have grown up in a dysfunctional family which unfortunately can lead to this as well. Her defense mechanisms are just way out of whack.
I do agree that you should see a L. For you S2 sake. If you wife is saying things and acting out in front of him it would be better to know what rights you have to protect him. That is not to say that your W is not a good mother but I am sure even at 2 your son is feeling the effect of the irrational behavior.
Your wife is trying to get back at you so she won't take your son from your arms, but imagine how that must make your son feel. He probably doesn't recognize that and only sees his mom not caring enough about him to reach out for him. She really is doing more harm than good. And she is telling you you don't care about your S???
I don't think there is anyway you can possibly address or get through to her. If something is really wrong, you would be the last person she would listen to and anything you say she would find offensive. Luckily for my friend his wifes family addressed issue with her and she got help. But it doesn't sound like your wifes family would recognize that she needs help if they themselves need help as well.
Best of luck to you. I will keep you in my prayers.
