Your parents will learn. If they don't, either educate them or ignore them. A lot of the bias is slowly going away more and more each year. I have a long history of MD's in my family, including my father. My brother and I are both in DO school, and I thought we might get some backlash from family members but they have been surprisingly supportive. My dad was ecstatic that I got in to medical school, he didn't care which one. I honestly think he was most happy that I got in to a school in my home town. He never pushed me to MD or DO. Just whatever I could get in that would be the best fit for me. He actually is a residency director at a local hospital and prefers the DO students over one of the major local MD programs.
Something that really surprises me is that despite my dad's unbiased opinion on DO vs. MD, he doesn't have near as much respect for nurse practitioners or PA's (by that I mean he scoffs at the idea that they are qualified to do everything a primary physician can do). If it was up to him, nobody in my family would ever see one. My mother actually had an appointment at the doctors office and instead of her doctor it was a PA, and she left.
Parents are stubborn. Just be happy that you are going to be a doctor. Rankings don't matter. Get in to a school that you like and do your best. You will be a doctor no matter where you go. No sense in getting upset about where your school falls.