Danielle-I agree with Nita Ann and I would add that for several years, I was part of an Al-Anon group for children of alcoholics. In your case, you don't say alcohol had a part in your step-parent's issues, but being in a 12-step program helped me focus on how to deal with the issues and emotions involved in letting go of the abuse and the abusers. There are other 12-step groups, even Overeaters Anon. I'd recommend checking one out or seeing if you can get a hold of some of Al-Anon's books. My heart goes out to you and I'll keep you in my prayers.
I also want to add that I think you're doing incredible in your weight loss! It's inspiring to see someone who's come so far and is still working a plan successfully!