If you have a terrible childhood, when your parents are old and decrepit, should you help them?

My father abandoned us as children. However, we have memories of his mother, old and needing help, and how angry and abusive he was to her. When she came over and we were small children we still remember his yelling at her, his anger about having to drive her around for shopping, about having to help her at all. He is old now and my sister and I visit him, have taken care of his estate, and bring him goodies all the time. My sister’s husband, who treated his own mother in this way before her death, thinks we should do nothing and let him die alone with no one. I think that’s wrong. What do you think?