Question

The tyres of heavy vehicle are double layered

Answer 1

yes to control the weight

Answer 2

The overall weight of the vehicle is distributed with some ratio between the axles. For handling and maneuverability it generally makes sense for the front steering axle to be very close to the front of the vehicle, while most of the cargo load is carried towards the back of the vehicle, both between the axles and overhanging past the rear axle. A greater fraction of the load is therefore carried on the rear axle, and in order to keep the ground pressure within reasonable limits, a larger contact patch area is required. The construction of pneumatic tires makes it difficult to make one that is very wide relative to its profile height, so putting two narrower tires next to each other is easier, and provides some redundancy in case one fails.
Putting dual tires on a steering axle would reduce the ground pressure there, but it would greatly increase the effort required to turn the wheels, and would result in a high rate of tire wear. A compromise that is sometimes used is to make the front tires significantly wider than the others.