There's still some important information missing from these reports, mainly the type of vehicles involved. Why does that matter, you ask? Because the type of vehicle "D" was driving was a large crew cab 4-wheel drive truck. The type of vehicle the other "British" folks were driving was also a 4-wheel drive vehicle. I do not know the years or makes of either vehicle, just that they both fit this profile.
The vehicles were what was being targeted, not the families. Large, 4-wheel drive trucks are the preferred vehicles for transporting loads of drug/human cargo across the border. These guys needed a vehicle and did not give up until they got one from the 2nd family.
A Lexus or a minivan is useless to these guys. So is a Jeep for the most part because of its limited space to carry a load. They need large pick-ups or SUVs like Suburbans with 4-wheel drive. They don't want your Nissan, Toyota, or Hyundai car. If you drive a car, your chances of being carjacked as happened in this incident are slim-to-none. If, like me, you drive a large 4-wheel drive vehicle (I drive a F250 crew cab with 4-wheel drive and an off-road package), definitely keep your eyes open and your guard up. That is exactly the type of vehicle they are looking for.
On the upside, it's much more difficult to physically stop or take these larger vehicles because they are built like tanks. I have no qualms about running somebody off the road in this situation... provided I don't have a bullet in my bubblegoose. The story "D" tells of being able to physically evade these guys proves my point. They don't want your money, your belongings, or your children. They just want the vehicle. Personally, I wouldn't let mine go without a fight, but that's me. Realistically, if bullets are flying, the best thing you can do is pull over, walk away from the vehicle and let them have it.