Apple has this thing called Legacy Contact which allows the same but then built in to the whole Apple account. This includes devices as well as the iCloud ~~and attached keychains. Granted, it is another hoop to jump through compared to presharing keys with each other.~~

It would be nice if your Apple account could be unlocked with some other keys as well apart from the primary one, but I guess that is what Apple calls the “Legacy Contact Key”.

Edit: okay so the keychain is excluded from this. So back to storing each others passwords in eachothers keychain…