It sounds like you haven't read about how it works. The system doesn't require the heir to verify their identity - you have already shared an encrypted form of your key with them, they just have to trigger the unlock timer to access the key they already have along with a signature from Casa's recovery key. It's basically just a timeout system that unlocks access to the key material that has already been distributed.

Of course not, that would make it custodial.

The mobile keys are only held by the client and their designated recipient.

For the ultra paranoid, we offer the option to use a second hardware key in lieu of a mobile key.