Apple has two related features, Activation Lock ( Activation Lock for iPhone, iPad, and iPod touch - Apple Support ) and Find My ( iCloud - Find My - Apple ), which are designed to prevent anyone else from using an iPhone, iPad, or iPod touch if it's ever lost or stolen. Deactivation of either requires knowing the Apple ID and password that set the feature, or by placing a special request to Apple to reset the device. This Apple ID information essentially defines the current ownership of the device.
Click on this link to learn how to remove Activation Lock --> How to remove Activation Lock - Apple Support
or this one for disabling Find My if activation lock has not yet engaged --> Turn off Find My on your iPhone or other devices - Apple Support
If you do not know the required information the device is useless to you unless you can get the person who inherited the items to get control of the account as outlined in this document: How to request access to a deceased family member's Apple account - Apple Support