Here are the Apple support pages that outline the Activation Lock - and the only mechanisms by which it can be turned off:
https://support.apple.com/en-us/HT201365
https://support.apple.com/en-gb/HT201441
As you will discover, unless you are the owner of the AppleID that was last used to activate the device, or unless you can secure the cooperation of the previous owner, you’ll not be able to defeat or bypass the Activation Lock. Without documentary evidence that you are the original owner (such as sales receipt showing the serial number), Apple won’t assist - and nobody here will be able to help you.
If your brother is the owner of the AppleID that previously activated the device - and the associated AppleID or password are forgotten, your brother can recover them here:
https://iforgot.apple.com
To recover the credentials, you’ll need access to one of the following:
- The primary email address mailbox that corresponds with your AppleID
- Any of the secondary/recovery email addresses that should be configured for the AppleID account
- Any of the trusted telephone numbers (fixed line or Cellular/Mobile) that are associated with the AppleID
Unless the AppleID account has not been fully/correctly configured, or has been seriously neglected, recovery of the AppleID and password should not be difficult.
More information about recovery of your AppleID:
https://support.apple.com/en-us/HT201354
More information about recovery of your AppleID password:
https://support.apple.com/en-us/HT201487
When you recover access to the credentials, you would be well advised to log-in to your AppleID account from a web browser - and verify/update any email addresses and trusted telephone numbers:
https://appleid.apple.com