Shaun80, WhiteShark is spot-on in that you cannot change another person, their behaviors, or their perceptions.
You didn't produce the children in this relationship - they are not your legal responsibility, nor are they your offspring, even if you have come to love them and care for them. You cannot "save" those children, nor is it your obligation to do so UNLESS you want to get involved in some sort of quasi-custody battle, which I promise that you don't.
Since you were wise enough to avoid a legal, binding contract of marriage, you can walk away from this situation without any hassle other than taking YOUR belongings, and never looking back. You have that option, and it is probably the best option that you can choose where this woman is concerned.
In this world, there are "good" people, "bad" people, and people who are just lost. This gal is dangerous to the mind, body, and soul. Do you really want to risk all of this for some unrealistic sense of obligation? "Love" doesn't even factor into this situation - "love" is not cruel, heartless, demeaning, or risky.
Run.........run, run, run, run. And, once you are well and away from this woman and her children, contemplate some individual work to figure out why you became involved with someone who used and abused you in such a way. I made 2 very poor decisions when I married 2 different types of abusers, and I spent the best part of my life in a state of fear, loathing, and desperation. What came after that was almost beyond description.
So, you are young enough to sort yourself out, get your proverbial ducks in a row, learn to protect yourself, and choose a better partner, next time.