Unlock

Find My iPhone Activation Lock - This is a security feature, in part to deter re-selling of stolen devices. --> http://support.apple.com/HT201365

Turn off Find My iPhone Activation Lock (formerly: Activation Lock: Removing a device from a previous owner’s account) - An activation lock can only be removed using the log-in information for the account that applied the lock. --> https://support.apple.com/HT201441

How to request access to a deceased family member's Apple accounts [and devices] - https://support.apple.com/HT208510

If you are only trying to remove an activation lock you can try taking it to an Apple Store along with proof of identity, the original sales receipt for the device with the deceased's peron's name on it, and documentation (will) indicating ownership has passed onto you. There is no official policy about this.

Here are the Apple support pages that outline the Activation Lock - and the only mechanisms by which it can be turned off:

Activation Lock for iPhone, iPad, and iPod touch - Apple Support

Turn off Activation Lock – Apple Support

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.

However, that isn’t necessarily the end of the story...

A close Family member or Executor, with the required supporting paperwork, can make application to Apple to be granted access to the Apple accounts of the deceased:

How to request access to a deceased family member's Apple accounts - Apple Support

However, quite often, close family also have sufficient knowledge - and access to likely recovery paths - that access to the AppleID account of the deceased family member can be recovered. Having done so, it is then possible to release the Activation Lock that prevents reuse of an iPad/iPhone.

The following guidance is written from the perspective of the owner - but a family member will get the idea as they run through the process.

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

Activation Lock for iPhone, iPad, and iPod touch - Apple Support

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 any 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:

If you forgot your Apple ID - Apple Support

More information about recovery of your AppleID password:

If you forgot your Apple ID password - Apple Support

When you recover access to your 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/

Having recovered access to the AppleID account (and therefore the AppleID username and associated Password), Activation Locks can be removed. There are several routes to this, but for brevity, I’ll refer you to this support page:

Turn off Activation Lock – Apple Support

If the passcodes of any devices are unknown, the data stored on the device itself is now gone - but from your question I surmise that data recovery is not you immediate aim. That said, if the device(s) have an associated iCloud backup, you can restore the backup data to the device. To do so, you would need to follow this procedure:

If you’ve forgotten the passcode on your iPad, or your iPad is disabled – Apple Support

You’ll need access to either a PC (with iTunes installed) or a Mac (with iTunes or Finder - as appropriate for the installed version of MacOS). At the end of the process, you’ll have the option to restore data from the backup.

If your intent is to wipe/reset the device(s) for reuse by a new user, you would be best advised to prepare them properly:

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

I hope to have covered all the likely scenarios - and similarly hope that this guidance is helpful in fully resolving your current difficulties.

I was assuming the titles of the individual documents were self-explanatory as to details they might contain so to keep my response succinct I didn't bother to outline their contents.

Jeremy, you are trying to unlock a device where you are not the owner of the Apple ID. Methods for recovering forgotten passwords won't apply in this case unless you are very lucky and your relative used security questions to which you know the answers, or you have access to accounts and equipment used in Apple's Two Factor security measures.

If you intend to sell this device then by all means follow the instructions provided in the link about selling devices, just note that one of the major things that mentions is making sure Activation Lock has been disabled, so we're back to needing to solve your primary dilemma which I addressed in the first response to your post.

Limnos wrote:

Methods for recovering forgotten passwords won't apply in this case unless you are very lucky and your relative used security questions to which you know the answers, or you have access to accounts and equipment used in Apple's Two Factor security measures.

Others have demonstrated, on frequent occasion, that family members often have adequate insight and knowledge to recover the AppleID account of a close family member. It costs nothing more than a little effort to try. At worst, an attempt may be unsuccessful; likewise, the OP may have a successful outcome.

It is their choice to make the attempt using the comprehensive information already provided.