Get an experienced family law attorney involved to represent you. Let the attorney deal with the problems as they arise. You don't have the training or education to do this without professional help. Depending on the circumstances, you may or may not be able to accomplish an involuntary termination of the father's rights--the first step to a step-parent adoption.
I am not intending this to be legal advice, because I don't know the particulars of your situation. Call me if you would like to discuss this or other isues.