delete apple id

Ask you brother if it is his account. If it is, get him to do the things in this support article --> What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

If it is not his account, it appears that although the phone was "new" to you, it was not truly new. It had a previous owner who did not sign out. In that case try to return the phone to the seller and insist they do the things in the support article, or ask for a refund. You are encountering Activation Lock which inhibits the re-use of stolen devices.

If your brother did sign into it but does not have the information, or will not provide it, to sign out, Apple can completely reset a device if a person can provide sufficient evidence of valid ownership. Check the requirements and steps at: Activation Lock support request - https://al-support.apple.com/#/additional-support Apple says, "Proof of ownership documentation is required," but does not detail what currently constitutes proof other than it “must include the product serial number, IMEI or MEID.” Apple may typically require the original receipt* issued by Apple or an Apple Authorized Reseller. If Apple resets the device this will give you access to the device but won't restore access to the account used to lock it. There is nothing that can be done to expedite an Activation Lock request.

*Apple recommends you "Keep your receipt after you buy an Apple device" --> Keep your receipt after you buy an Apple device - Apple Support