It sounds like ether a pinched nerve or he's damaged a little nerve in his ankle, i would get it checked up because damaging any nerves in the feet can be dangerous, the feet is one of the most sensitive parts of your body and has artery nerves close to the skin, don't leave it unchecked in case he's damaged a nerve as it can cause clots in the foot.
You need to go to an emergency room for an evaluation and an x-ray. Don't fool around with this.
Your brother's ankle has fluid retention so when he presses on that area, it indents and then slowly comes back to normal.
If he is still having a problem with his foot in that it is painful and he cannot put his weight on it, get him to go and have it x-rayed or see a doctor to examine the foot.
In the meantime, tell your brother to strap up his foot to support it (not too tightly); he can apply a cold compress to his foot. This is done by either getting a cool pack or a towel dampened in cold water. Natural set yogurt applied to the swollen area will also help to reduce the inflammation and swelling. Only an x-ray would show if there is a break.
Tell your brother also to keep his weight of that foot as much as possible and when he is sitting down to elevate the leg.
Sprains to tendons and muscles can take much longer to heal that breaks to the bone which normally take about 6 weeks.