In that case, multiple thumb drives because they do go bad with instructions where to download 7-zip so they do not rely on Google and to use "the family password" to open a password protected 7-zip file. Plain text file inside that. Ensure everyone in the family know what they "family password" is by making use of it for something.

Keep the thumb drive tech up to date annually just in case the tech changes and they can't figure out how to use current thumb drive tech.

Have thumb drives and instructions replicated in multiple places in the event the home burns down or is otherwise destroyed. stored with other trusted family members that live near by or even at remote locations.

Avoid clouds, cloud accounts, any system you do not control as they can be hacked, go out of business, lose your data, accounts disabled upon death, accounts closed because who knows why, etc...