You can set up a server that requires an email sent to it every month before it will email your family members with instructions and the private key.
Possibly could make it a smart contract maybe?
Pity that you don't like my previously suggestions)
You can make easy. Right down an e-mail with everything and put timer 1 week (1 month .etc) on it. And if you are dont die in this 1 week (......) you just put a new date of sending.