Paper is a system that would have worked 30 years ago, unchanged to today. I think there's a reasonable chance that the same system would be working, unchanged, 30 years from now.

How many computer-based systems from 30 years ago are working unchanged to today?

Also, it's a system that any member of my family at any time in the past half-century from ages 12 to 98 could have understood. I think there's a reasonable chance that the same technology (paper & boxes) will be understandable for the next half-century, as well.

If you want to be updating a computer-based system for something as important as this every 5 years, that's fine. Everyone needs a hobby. But I have no guarantee that my family will be interested in or comfortable with it when it is needed.

Managing physical custody of something is just easier.

Any cloud solution is one credit card expiration away from destruction. Other solutions are difficult for loved ones to find.

I don't think I'd go as far as saying I'd never rely on a computer-based solution, but I am weary of putting all this extremely important information in a potentially vulnerable place. As a lot of people here are saying, paper might just do the trick.

So I guess for your purposes this means focus heavily on security. Keep us updated on how it goes!