Amanda, thank you for sharing your story and that of your family. Because its your family, i don't think you realize how much of a monster your grandfather was and how broken your mom still is. In a healthy relationship, a normal reaction would have been, for your mom to show some anger towards both of her parents & look your sister in the eyes and tell her she is sorry for the circumstances under which she grew up and for not being able to protect her.
The most shocking aspect of this film was the loving and respectful way in which everyone treated him up to his last few days. He was a child predator and an evil man and your mom had every right to be mad at him yet she shows him love. She goes as far as protecting him from you - telling him he doesn't need to respond to the messages his victims sent him.
The man committed crimes his entire life and got away with it because his family was there to protect and enable him. Sadly, your grandma could have helped get him locked up since his victims were so young and could not speak for themselves. Instead she chose to keep silent.
As a Dr. he had access to hundreds of children, all of which were probably victims of his abuse, all of which probably had their lives ruined. Even in his old age, he was unapologetic, even seemed to get pleasure talking about the abuse and rape he inflicted on children. It's shocking that time & time again everyone referred to his predator behavior as a "bad habit". Let's be real, sex with a minor is NEVER consentual, its rape and no toddler gets pleasure out of being abused. Yet, when he talked about abusing your mom he talked mutual pleasure - she was only 5 yrs of age! Absolutely no remorse for ruining her life is beyond sick & perverted. Why did no one tell him during the filming that what he did was a crime? Did you look into whether he was potentially abuse as a child?
Again, thank you for being so brave and sharing your story. I hope everyone gets the help they need so that you can begin to heal - especially your mom.