I know I am telling you something you don't want to hear, but I will say it for you to consider. One way Dad can avoid going through the whole legal process and having to fund it, is if you notify CYF. They will do everything and you will be less over whelmed, you will also hold the knowledge that other siblings will be protected. Ok, just saying this for you to have another angle to consider.
I know this is so big, so overwhelming, the only way it will be less for you to carry, is if you are able to share some parts that you are comfortable sharing with trusted people. (I know which part you don't want said, but there is other stuff around that too) This will really lighten your burdan.
Just know this, you have been so strong and so brave to put up with all you have endured, you may not recognise that right now, but you have been.