Found this map of their route... (reuploaded to imgur to save the little website I found it on from being slashdotted).
Perhaps things have changed :)
I used to be so much into this kind of travelling, I already feel like I hold back so much on what kind of trips/destinations we choose to do now because of kids.
I can't even imagine myself doing such a hardcore trip with 4x kids. It looks like they timed their pregnancies to be on locations with good healthcare but still these guys really are wonderers in the most beatiful sense of the word.
For what it's worth, even now the guide can ride along with you in your car, they don't necessarily need their own wheels.