My brother sprained his ankle, and now it's whole swelling. Will it become fracture? But he feels numb instead of pain

No. He could have a fracture. Sprains do progress to or turn in to fractures. The numbness is due to swelling. He needs to be evaluated and have x-rays done.
Probably Ligaments. A sprain occurs when ligaments are stretched beyond their limit. Your brother likely sprained, or tore, the ligaments in his ankle, hence the swelling. However, if there is any question of whether the bone itself has been fractured, it's time to go to the er to get an x-ray.
Get an x-ray. Twisting ones’ ankle can lead to a sprained ankle. Often times, this may result in ligament or tendon injuries which may lead to ankle swelling, pain, and possibly instability. An x-ray of the foot and ankle will be able to assist in differentiating a sprain form a fracture.