Hi
Activation Lock prevents unauthorised use of the iPhone if it is lost or stolen.
If the iPhone remains locked to your brother's Apple ID account, then it can only be disabled by him either entering his Apple ID and password on the iPhone or by him removing it from his devices list in Find My iPhone via iCloud.com. If you cannot arrange for either of these steps to be taken, then you will be unable to use the iPhone.
If your brother is having issues with his Apple ID credentials:
It may help to follow the instructions here:
If he still needs assistance, ask him to contact Apple Support or make a Genius Bar reservation, taking along the iPhone and his original proof of purchase for it:
- Contact - Official Apple Support
- https://twitter.com/applesupport
- http://www.apple.com/retail/geniusbar/
If the iPhone is pre-owned by someone else (ie other than your brother) and is instead locked using that previous owner's credentials, then it can only be disabled by that person following the same steps described above.
There is no way around this security feature.
More information and instructions: