You've thought about this. Every self-custody holder eventually does.
You need to document the location of your devices. The PINs. Whether a passphrase is in use and what it is. How to initialize a transaction. Which wallet software to use. What order to do things in. Where the seed phrase backup is. What not to do. And you need to do all of this clearly enough that someone who's never sent a bitcoin transaction can execute it under stress, grief, and time pressure, without making a single irreversible error.
But the moment you write all of that down, you've created a treasure map to your wealth. Anyone who finds it, whether a contractor, a cleaning person, or a break-in, has everything they need to take your bitcoin.
One of our clients, a yacht captain who carried hardware wallets across three continents, described it this way: “We were writing these treasure maps for our family, trying to document everything about the wallets and seed phrases without creating a security risk. It was impossible.”
Another client managed his own multisig for years. He eventually admitted: “The person who needed to know wasn't interested in learning.”