There is also a possibility that the family already knows something from LE that is not open to the public, but at this stage they have to keep it to themselves due to forensic reasons. We have no idea what they know and how much did LE disclose to them, but I think they know more details of...
Hope LE knows the answer and collects more evidences from the different camera, which is closer to the scene.
Also, YY immediately steps to the car as soon as it stops. I think this is because BC shouted (or beeped) from the car before it stops to attract her attention.
Very nice analysis for the surveillance video. I also watched the video many times, but could not find more useful information. It's possible that YY showed the map using her cellphone before she got into the car. But it's really weird that BC moved the car so quickly, within 4-5 seconds after...