You can tint your rear windows by 30%. You will need to go to Madinat Khalifa Police station and request them, they will add it to your vehicle permit after they check your car. They have no problem if you are a family man (hint - have a child safety seat installed at the back).

Then you can go to C ring road near oasis vehicles (something) and they can help you out with the tint.

All the best.