> is there any way to guarantee these heirlooms remain intact and available
Are they actually heirlooms? If the goal is to keep these safe so generations can continue to not look at them, what's the point? If you haven't looked at something in years, odds are nobody wants to look at them.
The actual object is less important than the exercise and the discussion. Substitute "photo albums" for "medical records", "civil certificates", "passwords + 2FA codes for all DeFi wallets" if you want.
The things you list need to be available for (at the longest) a month or two following my untimely demise.
The OP is talking about generational foolproof storage for photos which is both totally different and a slightly more convenient version of saddling your heirs with a closet full of photo albums and slide carousels.
As someone who was in Brazil and had to dig into records from my Portuguese great-grandparents when I was collecting documents to claim my citizenship, I assure your documents need to be available for a lot longer than you expect.
Are they actually heirlooms? If the goal is to keep these safe so generations can continue to not look at them, what's the point? If you haven't looked at something in years, odds are nobody wants to look at them.