I saw that the other day..
I have never been too concern when pulling doubles... I don't do it too often, but enough to be experienced..
I believe his first mistake was the truck he was using.. Looks like a 70's chev. That truck really is not adequate in the first place.
I wonder if he had anti-sway and equalizer hitches on the trailers. That would also make a big difference.
The driver stated that he felt the trailers start to sway, so he used his brakes.. This is a bad idea also. (assuming he used the pedal, and not just the trailer brake controller)
But it is easy for me to sit and say everything he did wrong, because this is the internet, and I know everything.. about everything....
In reality, for all we know he had all the right equipment, had plenty of experience and know how, and this was just a freak accident.. Could have blown a tire, etc.
Over all, I think it is a crappy situation, and feel bad for all involved.
Edit: and after looking closer, he did at least have an equalizer on the first trailer..