Two routes you could take:
1) The process designed for this unfortunate situation --> How to request access to a deceased family member’s Apple Account - Apple Support
Apple says:
"While we may also be able to help remove Activation Lock from devices that use your loved one’s original Apple ID, their iPhone, iPod, and iPad will need to be restored to factory settings before they can be used with another Apple ID. Please note that devices locked with a passcode are protected by passcode encryption, and Apple can't help remove the passcode lock without erasing the device."
2) Apple can completely reset a device if a person can provide sufficient evidence of valid ownership. Read the requirements and steps for an Activation Lock support request at: https://al-support.apple.com/#/additional-support and links at the bottom right for the type of service requested. Apple says they “may” require "proof of purchase documentation” and that you need “proof of ownership documentation”, but does not detail what currently constitutes proof other than it “must include the product serial number, IMEI or MEID.” User reports on this community indicate that typically Apple will absolutely require, and ONLY accept, an original receipt issued by Apple or an Apple Authorized Reseller. Presumably this is the only kind Apple can authenticate against fraud since Apple is not involved in third party sales. Apple recommends that you "Keep your receipt after you buy an Apple device" --> Keep your receipt after you buy an Apple device - Apple Support
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.
My commiserations.
