The key here is that they already have a login, so they can do the normal "forgot password" or whatever if there's any kind of complications. Since they're joint owners, nothing changes with account numbers and whatnot if I die, whereas if they were simply a beneficiary, they'd get a new account number and have to go set everything up again.

I wrote a cheat sheet years ago, and this should dramatically simplify it. I'll just point out what the purpose of each account is and what automatic transactions are there and that should resolve most of the questions my SO might have, at least financially.

The rest of my schenanigans however... may god have mercy on their soul...