This question is deep, well for me my younger brother has access to my crypto assets so if anything should happen to me he will take charge of my assets
But, we have seen many cases where the brothers robbed and broke away for property, so could you really trust your brother? Won´t your brother exchange you for a property? Cryptocurrencies should be automatically transfered to brother´s wallet after some time of inactivity, like 1 year. That will solve many problems in your fraternal relationship.