The Kia Classic NGV on a full cylinder can go all the way from Karachi to Hyderabad (i.e 151+ Kms) on AC! Unfortunately the consumption in the city is mostly around 70/80 Kms on AC. Its pretty much the same as my Mehran VXR on CNG. I'm telling you this as I currently own a used Kia NGV 2002 model and I have no complaints about it as of yet. There is no trembling at 120Km/h, the brakes work fine, the pickup on AC is amazing.
As far as your fear of the rear going down, I just had some work done on it by adding some sort of 6-inch thick rubber parts which go on top of the springs. Afterwards, I had no complaints about the rear going down as the car's rear stayed up after that and I took my family to Hyderabad then.
If you have a family of 6-7 and intend on keeping this car for a good period, then go for it. I have found in my experience to be a great car with all the space I could get in any other expensive sedan. So long as if you are getting a used one in a near remarkable condition.