First, your Mom is amazing. What a great great mama. You are more than fortunate. I would have given anything for my mom to be so smart, wise, and a good fighter. She got you away from a bad situation and found a good man to help raise you and your sis. Frank did you a favor by getting out of the picture. He was not well and would have damaged you and your sis even more. He did the right thing, even though it may have not been for the right reasons. Try not to think about him too much. Just concentrate on your nice life right now and live in the moment. Do not have any false notions about Frank. Be realistic.
Be grateful you have a good daddy at home and look to him for a male role model. Being a daddy is earned, not granted by biology. You have a good dad and mom and just focus on that and make the best out of your life. All of you are doing a bang up job! I loved your story and continue the good work. That is just great!