I agree with the above comments. The shape of your head determines which helmets fits best. You don't need to spend a fortune to get high safety specification, my cheap Duke 2 actually outperforms my expensive Schuberth on safety ratings. But the Schuberth is more comfortable and quieter.
Do not buy online. Helmets need to be fitted by someone who knows what they are doing. An experienced biker can buy online and return an unsuitable helmet, but your brother won't have the experience to do that.
If you live near a branch of Sportsbikeshop they are excellent. I buy helmets from J&S as there is branch just round the corner. They are also good, their prices tend to be higher but they offer a price match so you can get them to match Sportsbikeshop's prices.