Quick skim through my rulebook, I'd say 1
KP for the Unit, based on:
Most vehicles fight as individual units and are represented by a Single model. However, some small vehicles. like Ork Warbuggies and Eldar Vypers. operate in units of more than one vehicle, known as squadrons. These follow the rules for normal units, with the following exceptions:
Emphasis mine. There is no exception mentioned about each Member of the Unit (Squadron) giving a Kill Point Each, so Its safe to say that you have to kill all the members to earn that kill point.
Now that being said, its 0650 at time of writing, and I am a total newbie on these here forums, so don't take my word as Law™