Cars can't go to Siri and Paya. It is a kacha jeep trek can be muddy in rains..
Upto Naran, road is superb.
Petrol is not a problem. Naran ma petrol pump ha. Mansehra and Balakot ma bhi petrol pumps. So no need to worry about petrol
Get the tank full, as where you see a pump...
Between Balakot and Naran, there should also be petrol thruogh some shops or local petrol dealers.. not much sure..