Leaving Bitcoin as inheritance process is more harder than leaving physical properties or fiat as inheritance. Many method has been suggested under this thread and I'll suggest the private keys should be printed and included in will. Or get an hardware wallet, keep it in a secret place like a small vault including the details, then include the hints in your will.
I don't know what guarantees there are that your keys won't be revealed until the time of the inheritance. But this is an interesting position