Nice little animation here which shows what the limo stop (really a rolling stop) would have looked like from the Willis family position. As you can see, if you are behind the limo (like the Willis family) a slowing limo will look as though it is stopped. This is due to the perspective from an angle looking at the limo from behind:
Good animation. Yes, it was not a limo stop. Not really a rolling stop. It was a slowdown from 13 mph to 8 mph. From that angle, slowing from 13 mph to 8 mph will look pretty close to a full stop. Plus, some other vehicles, closer to the Willis’s, did stop.
There are good reasons to doubt eyewitness reports. A slowdown, not even cutting the speed in half, can look similar to a stop from certain angles. The “Crack-Thump” of a supersonic bullet, the sound of a bullet fragment hitting the limo, or even echoes, could confuse a witness into wrongly stating the number of shots and the spacing of the shots. Witnesses can be influenced by what they heard others say about an incidence, which could be incorporated into their memory. Not to mention that a witness can be wrong for no obvious reason.