Give them first a time to mourn. Even they don't have ideas on what will you supposedly told them, in a conditioned and relaxed mind, they will learn how to do it. There might be some close friends to them who can help and knows this bitcoin thing.

Does your friend living close to them know this bitcoin stuff? If yes, then good. Tell the family that someone is willing to help them. If no, then let your friend not be involved here.

But remember, when the time comes now that you need to tell them about bitcoin, just assist them "if they told you to do so". Don't say right away that you will help them access it.