This may be a little late, but I would suggest, if you're comfortable with it, that you sit down and have a serious, calm discussion with your father, and make a point of asking the question, "how would it have made you a bad parent to let your son sleep on a park bench, but make you a good parent to let your son who raped your daughter continue to stay with your daughter?" or "How is it ok to endanger your daughter by protecting your son who raped her?" or something along those lines. And I don't know your father, so if you do feel comfortable asking him a question like that, be prepared for a strong, potentially unfavorable initial reaction.

I know these might seem like very blunt questions, and for that reason it's important that you don't ask them in a way that suggests you believe your father is the villain here, regardless of your feelings about that. If he feels as though he is being attacked, he may decide he doesnt want to have a discussion about it.

The reason I believe asking him a question like this would be beneficiail is because it may answer some question you have about it, and may settle some feelings of injustice I'm sure you have been holding onto (and rightfully so) since this all happened. If you decide to have this discussion, be prepared for the possibility that the answer he gives you may not satisfy you, or may even initially cause more hard feelings. Again, I don't know your father so this is difficult, but the most difficult discussions to have are often the ones that need to be had. If these issues aren't addressed, you may end up with festering emotions that could drive the two of you apart in the long run.

I really hope this helps. And I'm sure you know this but I just want to emphasize that there is no reason for you to feel any sort of shame or guilt or embarassment, and that if anybody ever felt disgusted with you in finding out about this, that is due to their own issues that they should deal with, and has nothing to do with you. I know it'll probably take a while for you to be able to internalize these things but I felt like it should be said. And those douche bags PMing you are probably the types of people who need to be sent to prison.