Hi,
I'm quite new to Drupal and I'm doing quite a big project in it. 
I'll try to keep my questions as short as I can. I wonder if anyone can help. This is my scenario..

I have a hierarchy something like this:

Region 1
-- Vehicle 1
---- Driver 1
---- Driver 2
-- Vehicle 2
---- Driver 3
---- Driver 4
Region 2
-- Vehicle 3
---- Driver 4
---- Driver 6
-- Vehicle 4
---- Driver 7
---- Driver 8
etc

On the submit form, I have an active select that once Region is selected, it filters the vehicle list, which then filters the Driver list
My question is, how do I add, say, a "Co-Driver" (who will be at the same level as the Driver)?

In other words, once someone has selected the Vehicle, I need there to be 2 lists (dropdowns) that are filtered with Drivers and Co-drivers. 
I hope that makes sense!

Any help would be greatly appreciated. Thanks!


Kind Regards,

Graeme McKibbin
Software Developer