Please note -
01. The Prospectus/Catalog of the Car which your parents were driving and the medical reports of your parents are more than enough to approach the consumer court asking for the compensation which your family truly deserves. All that is required to be proven is -
(a) the airbags were faulty,
(b) your parents were having seat belts on themselves while driving the vehicle.
02. The company usually do not entertain anyone at the time of inspection of the car at their workshop. If you want your presence to be over there then you may specifically ask for it from them.
03. Your filing of case is not dependent upon inspection of car from the side of the company so you may chose either of the option like filing it after the company has completed its inspection or before the company has completed its inspection. However, if you wish to play safe then you may chose to file your case after the inspection as that closed down all the remaining speculation about the faultiness of the car.