My neighbor double parks blocking her sidewalk and entry to my driveway, illegal?

I have a licensed day care in my home which is at the end of a cul-de-sac, my neighbor torn out her driveway and never replaced it and for almost 2 years has been parking across her driveway and double parking which blocks entry into my driveway. Parents dropping off children have to make an unusual deep curve to get around them but are unable to back out without fear of hitting their double parked cars. Also in the winter backing out of my drive I only have about 6 inches clearance when turning my wheel to clear hitting their car. Not to mention I have came home at 10pm from training only to find I can't get into my driveway because of them. I have asked at least six times and they always seem to point to its the other neighbors fault. I always tell them no its you whose car is leaning into my drive. I don't like to argue with my neighbors but I am getting complaints from the parents about always having a problem with the parking. Is it illegal to park across your sidewalk which blocks anyone walking or riding their bicycle. I live in Fairfax County, Virginia.