If the accident happens on private property, many road rules do not apply. The crossover to the road is normally a 'road related area' and covered by road rules.
For an accident on private property, accident rules apply (eg swap name and address, help injured party etc) however it will normally be the fault of whichever car was moving at the time of the accident unless one car is attempting to avoid the other. If both cars are moving towards each, both are at fault.