Glad to hear everybody is okay.
As mentioned, airbags don't always deploy, it depends on angles, deceleration rate (rather than speed), if seatbelts are on etc.
The airbag has to know if you've slammed on the brakes (you're slowing down) or you've hit something (impact). However it can't work on just one or the other, otherwise the bag would go off if you touched another car when parking, so it needs a minimum speed as well.
The usual figures (and this has a lot of variances) is about 10-16 miles per hour minimum speed before impact, and around 7Gs of force (there is a big diffence between an immediate stop, hitting a tree for example, or a car coming in opposite direction, and rear ending a vehicle in front, it's all to do with transference of energy, which gets a bit complicated, especially at this time in the morning
Vauxhall can plug the car into their diagnostics machine to see why it chose not to deploy, but you will need a main dealer to read this, a standard fault check will just do that, look for faults, you're looking to see what the controller has stored and you don't want this deleting. The insurance company might want to check as well, to make sure that the airbag is working as it should, that the self test works, and that one is actually fitted (it has been known for places to buy cheap cars with deployed bags, fit a new steering wheel cover and put a trick bulb in the dash which just lights for a few seconds when power is applied, no one knows until its needed that a VERY expensive airbag isn't fitted ).
In the end, everyone is okay, the rest doesn't really matter.