Apple can completely reset a device if a person can provide sufficient evidence of valid ownership. Do this online at: Activation Lock support request - https://al-support.apple.com/#/additional-support (Apple provides a specific link for contacting them about this service.) Apple says, "Proof of ownership documentation is required," but does not detail what currently constitutes proof. Prior to this new online service Apple typically required the original receipt issued by Apple or an Apple Authorized Reseller and documented provenance (so typically it would be the original owner who does this, or a descendant with legal proof of ownership). This will give you access to the device but won't restore access to the account used to lock it.
Apple recommends you "Keep your receipt after you buy an Apple device" --> Keep your receipt after you buy an Apple device - Apple Support
To your second question about how to deal with this in the future, you may wish to explore enterprise level management options from Apple:
If you’re an administrator and want to set up supervision, use Apple Deployment Program, Configurator 2, or Apple School Manager to set up your devices. (related post: This phone was bought by an organization … - Apple Community )
Apple Platform Deployment --> Apple Platform Deployment - Apple Support
Overall enterprise services
Apple Business Essentials --> Intro to Apple Business Essentials - Apple Support
Apple Business Essentials includes all the features of Apple Business Manager and more. Apple Business Essentials is one complete subscription that seamlessly brings together device management, 24/7 support, and cloud storage so your small business can easily manage every employee’s iPhone, iPad, Mac, and Apple TV (that your organization owns)—every step of the way. Apple Business Essentials is currently available only in the United States."