First of all, your keys should be in a usb for maximum security. Show the usb to your relatives without giving them access to it, either by hiding it or by placing it somewhere safe.
Then explain that in case you die, your crypto keys will be in there. Ideally you could teach them how to use them, but yeah... not simple.
Yeah nice suggestion... Been thinking on the same lines too.
Store all private keys on a dedicated pendrive and name it's owner in the will.
Also add a pdf file explaining how it all works properly.