Ask yourself this question : How are your other assets and wealth being handled at the moment? You use a Will, right? I would suggest that you make it a riddle that only your family would be able to understand and put it in your Will.
The Passphrase could be the answer to a question that only your family would be able to answer. Example :
~ Where was our first family holiday.
~ What was the name of our first dog.
You also hide the paper wallet < Metalstamped seeds/keys > in a location only they will know about.
~ Lemon tree at the orchard.
Do not use safe deposit boxes, because they are raided regularly by banks and thieves.
The Passphrase could be the answer to a question that only your family would be able to answer. Example :
~ Where was our first family holiday.
~ What was the name of our first dog.
You also hide the paper wallet < Metalstamped seeds/keys > in a location only they will know about.
~ Lemon tree at the orchard.
Do not use safe deposit boxes, because they are raided regularly by banks and thieves.
I always found these security questions funny. I know first names of many pets from multiple families. And by now, a family holiday would probably be documented with pictures on Facebook
You can also more often then not, ask people those security questions and they would very gladly tell you, even if you are a stranger to them.
You need to use something that is considered atleast kind of secret in the first place, something that you won't just show to anyone or tell anyone.
However the most useful thing is to just make a password with your family, that would be the most reliable and quite simple way. Or as with the will, use the multisig with the person you are leaving the funds to and your lawyer, if your lawyer is hip to that.