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Printing the photos won’t help much. After 20 or so years they are all discolored. You can’t prevent that.
I think SSDs might be the best storage medium for you. Consumer-grade ssds have a 1 year data retention when powered off. That means at least once per year you have to turn it on and copy the data around one time to refresh the cells. This way it’ll probably last several 100 years.
You can’t exactly make it fool-proof. Outside people will never know what you did to create your backup and what to do to access it. Who knows if the drives file system or file types are still readable after 20 years? Who knows if SATA and USB connectors are still around after that time?
For example it is very likely that SATA will disappear within the next 10-15 years as hdds are becoming more and more an enterprise thing and consumers are switching to M.2 ssds.
SSDs are by design less susceptible and more robust. No moving parts and able to work in much harsher conditions than hdds will ever be able to. The standard set by JEDEC requires every consumer ssd to have a 1 year data retention while powered off at 30 °C (I think). That’s the minimum it has to archieve but usually they are better than that. Do not buy the cheapest thumb drives because they contain the all the crap that wasn’t good enough to make ssds from it.
Btw you need to fire hdds up regularly too or the motor gets stuck. I think every 3-6 months was the recommendation.
Don’t make it flat every 5 years. Let a software monitor the SMART values of the drives and send notifications if the values indicate an increased change of a dying disc/ssd.
Those are the first that fail, followed by the usb controller chip in the tray. Keep it as simple as possible. Removable trays are probably the best way but I’m not sure how much wear they can take.
Do not buy 2.5" drives. This class will die out soon™. There were no new hdds introduced in years and ssds are often replaced by M.2 ones because of the faster connection.