Your fundamental problem will be the Activation Lock that will inhibit use of the iPad. More of this shortly.
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
You should note that if successful, this process will grant access to some information stored in iCloud - but will not, of itself, resolve access to the iPad.
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.
—
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
More information about recovery of the AppleID and associated Password:
If you forgot your Apple ID - Apple Support
If you forgot your Apple ID password - Apple Support
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 will be beyond reach. The iPad uses an encrypted filesystem, the Passcode being required to unlock the Secure Enclave (this iPad security chip) within which the only copy of the encryption keys are stored. Without the Passcode, the encryption keys cannot be accessed - and neither can the data that the keys protect. 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 Windows PC (with iTunes for Windows 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.
I hope to have covered all the likely scenarios - and similarly hope that this guidance is helpful in fully resolving your current difficulties.