person has passed away and I cannot unlock the activation lock

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.

In fact there is a method in place for the specific case of a deceased owner. However note that it requires getting a court order, and knowledge of what the Apple ID is (though not the password). Please see:

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

I have this same question regarding my sister-in-laws phone. My wife would like to activate her sister's iPhone. We can provide a death certificate. Can you provide instructions how and where to go about this process? Is the phone tradable for a newer model?