Out of everything, I am sorta interested in seeing a redemption arc for the sister, not that she deserves it but that she is the sole reason Leslie was able to be saved from the fire. Even if it was out of selfishness of not wanting MC to use her power and dethrone her place in the house, I feel as though she could grow into a real character. She deserves hardships and struggle, but I would like to see at some point in the distant future that she whole-heartedly apologizes to her little sister for everything she has done. I believe you can't make up for the past but she can sure as hell try, MC doesn't even need to forgive her at that point nor would we need to focus on the sister anymore aside from a background character doing attempting to be a better person then they were previously... but maybe that is a bit much to ask.
As for the Dad... well, I feel like we won't be seeing any more of him in the near future...