They cannot accept the fact that their son was impaired and he should have used his head and stayed in the car. Not to be a jerk or anything like that but that was something they should have drilled into their son's head from the time he first started racing. Stay in the car. Most tracks have that in their rulebooks for obvious reasons.
If not Tony Stewart then it could have been any other driver out on the track that night. Would they be suing that person?
As far as the video goes, a camera can only pick up the sound directly in front of it not almost a quarter of a mile away where the incident took place. As for swerving, most racers, especially sprint car drivers will tell you, are trying to adjust their cars by moving the wing, adjusting brake bias or shifting weigth. Yellows are the perfect time to do that. And, the track is very dark on the back stretch. Visibility can not be very good when someone in a black racing uniform is standing on the track.