activation lock

Your Uncle will likely find the following guidance to be helpful is resolving any difficulties with the required AppleID - necessary to facilitate subsequent recovery of the iPad with which you have a problem...

If your device is Activation Locked, this help page will provide most of the information that you’ll need:

https://support.apple.com/en-us/HT201365

If you have forgotten your AppleID or associated password, these can be recovered here:

https://iforgot.apple.com

To recover your credentials, you’ll need access to one of the following:

• Your primary email address mailbox that corresponds with your AppleID
• Any of the secondary/recovery email addresses that should be configured for your AppleID account
• Any of the trusted telephone numbers (fixed line or Cellular/Mobile) that are associated with your AppleID

Unless you 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

After recovering access to the iPad, assuming that you manage to do so, you would be well advised to then prepare it properly for reuse:

What to do before you sell, give away or trade in your iPhone, iPad or iPod touch – Apple Support

I hope this information, insight and guidance proves to be helpful in resolving your problems. 

Tell him to use Apple's iForgot service or contact their Account Security team, or the iPad's original owner to supply Apple with its purchase receipt and ask them to remove the lock.

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