Regarding the concern about using the coins but not updating a private key with a lawyer or safe deposit box, this is not a problem if you have a deterministic wallet.  I believe the latest version of bitcoin core will create a deterministic wallet if you don't already have a non-deterministic wallet.  Several other wallet softwares will as well, and I believe all hardware wallets are deterministic.  To be clear, a deterministic wallet is a wallet where each subsequent change (and/or receiving) address can be unlocked from the same root key/password.  In other words, you only need to store the information once, and anytime a wallet is re-generated from it, the remaining coins will be spendable.

Regarding the concern about involving a bank or lawyer in general, it has been a few years, and I have not had any luck finding the service even though I want to, but I once read about a service that stores whatever information you want (I say information, not data, because I believe they store the data in a secured database vs storing individual files, and the service is really meant for passwords and account information) in an electronically secure manner (supposed to be secure from hackers and disasters) for release to designated persons upon your death.  Obviously this would not be a zero-knowledge service, so there would be some third party risk, but in order to do the same thing with a zero-knowledge service and not still involve a third party to protect a password (something you know in 2FA terminology), it would be necessary to secure that service with something you have instead or as well.  Unfortunately, I don't think I've ever seen anything secured with zero-knowledge using something you have for security.