Your brother's friend will have to remove the lock. The friend either needs to regain access to the old account, or present Apple with the original receipt for the purchase of the phone so they will remove the lock.
This support article has information about Activation Lock on your Apple Watch and how to turn it off. --> About Activation Lock on your Apple Watch - Apple Support
- Apple can completely reset a device if a person can provide sufficient evidence of valid ownership. Do this online at: Activation Lock support request - https://al-support.apple.com/#/additional-support Apple says, "Proof of ownership documentation is required," but does not state what currently constitutes proof. Prior to this new online service Apple typically required the original receipt issued by an Apple Authorized dealer and documented provenance (so typically it would be the original owner who does this, or a descendant with legal proof of ownership). Apple recommends you keep your receipt after you buy an Apple device. --> Keep your receipt after you buy an Apple device - Apple Support