And if I remember right the camera in the tunnel was said to be not working at the time of the crash....
So no visual confirmation of anything including the speed of the car.
How fast were they traveling? Well, fast enough to do this:
I'm no crash expert, but that's not the result of a 10 mph fender bender.
But fine, I'll buy your counter. Let's say they were sitting completely still with the engine off in that tunnel. Explain how a driver can "quickly turn round and release the seat belts of the other three". Try it.