Install a hardware keylogger inside your keyboard (or just buy an external usb hardware keylogger -- this is less secure for the paranoid) and have the password that accesses the keylogger written on a piece of paper with instructions on how to use it in your wallet. Tell your relatives that you have a keylogger in (or attached to) your keyboard and that instructions on how to use it can be found inside your wallet if you die. Run a monthly script that simply types all of your passwords out one by one in a notepad so the keylogger catches them. If you die, your relatives will find the piece of paper, access the contents of your hardware keylogger, and collect all the information.
If you are paranoid about someone breaking open your keyboard, stealing the flash memory, and somehow accessing it contents, I'm sure you could put an encrypting stage between the read and write stages (given you are making this keylogger yourself with a microcontroller). ...Or you could just use an online service that holds sets of passwords and secures them with a master password, but that's not as fun, is it?