AC Coaster will definitely be a better option. All the family members can have fun during the journey. And it will also be cheaper if you compare fuel cost of 4 cars as most of the time, you will have to travel on Petrol. You can hire one at around 6000 per day along with the driver. Diesel will be your responsibility and its average would be around 5 km/liter with AC running. As far as route is concerned, you can take N5 from Khi to Lahore and then M2 for Lahore to Rawalpindi. Or you can also take Khi to Khanewal on N5 and then Kbirwala-Jhang-PindiPhattian-M2 route to subtract some 100 kms but I always prefer the throughout N5 route. You can find good hotels in any big city on N5.