Don't think this is just Alabama. It happened to my friend in California. Why do you assume your step-siblings would be so mean? Other than that, you're screwed, my friend. However, you should thank God that your Mom has a place to stay until she passes.
My stepbrother might, just MIGHT be reasonable. He and my Mom speak on the phone weekly even though his Dad died years ago. My stepsister on the other hand is a wacko who has hated my Mom from day one cause her Dad married her within months of becoming a widower.
Both are extremely wealthly in their own right and don't need the money that the house would bring them. To them its pocket change.