With planes being long enough away from the demonstrator, and speed of sound relatively low (about 330 m/s), the booms of all three planes should be separate enough, e.g. a good 100 ms away from one another, even if all three went supersonic and were dragging their respective shock waves.
The distance between the planes appeared to be around 30-50 m at the supersonic transition time, as much as I can estimate the size of the planes. A sound recording made under the flight path should allow to measure how many dB was the demonstrator's boom.
Raises more questions though, because there were two other chase planes. Did the other planes stay below the sound barrier at all times?
Edit to add: Was no audible boom expected because of the planes themselves or because of where the people were watching from?