I think your ptsd started when you were walking the dog for an older man, even though you were young, you knew the porn he wanted you to watch wasn't right, and you felt uncomfortable when he was staring at you. None of this is your fault, you were a child walking a man's dog because you were told to do so by adults. And this older man lured you in to his perverted world and used his dog to lure you in.

The truama of having to watch porn with him has affected you then, as it is today, he was grooming you and he has also made you think everything is your fault, this is what abusers do, and so the abuse continued in the family home, with your brothers, you got raped, and now when you see naked women, your mind goes back to being in the old man's house where you were made to watch porn.

All I suggest is therapy, get some counselling for this. And perhaps, through counselling, you'll begin to realise that your the victim in all of this and nothing was your fault.