Heavy haul question

Watched this video on a facebook post...

https://www.facebook.com/share/v/1CRMWQ5Hao/

Can anyone please explain to me what exactly is going on? Why the two tractors behind the load and one in front?

I'd expect more in front to help pull, but I know absolutely nothing about heavy haul. Are the two in the back pushing? How does one actually even push a load? It's it to help steer the back of the trailer? If so, why two instead of one tractor?

Any explanation of this set up would be much appreciated. I'm in awe, not so confused.