[...] But I would also backup the private keys for each address with <1BTC. [...] I would have created detailed instructions on how to access all these Bitcoin (1. With hardware wallets, 2. With Seed Phrases and passwords 3. With individual private keys in the worst case scenario), and trained my wife, and eldest child on the procedure.
BIP 32 was invented for this reason. It is the default for Bitcoin Core wallets, for this reason. It is the standard of all reputable wallets, for this reason.
You do
not need to back up private keys individually! One seed backup suffices to back up a whole tree of hierarchical accounts. Unlimited wallets.
This is a safety issue. For the same reason that keypools are hazardous and harmful. Multiplying the number of things that you need to back up tends to result in loss of funds, sooner or later.
That’s a basic safety feature; BIP 32 was developed after it was discovered that, in the nitty-gritty real world, keypools are a money-destroying misfeature.