Bitcoin has had multisig wallets for a long time: https://en.bitcoin.it/wiki/Multi-signature

So it's not that hard to distribute several keys of the multisig to various heirs, who would have to agree on any transfers of funds. Another option is to keep each key in a different safe deposit box, with a will stating who gets access to the boxes.

Even with that, who do you trust to actually do any real transfer of your bitcoin in a fully secure way? Certainly not your lawyer, legal offices carry so many security problems. With a total of $1 billion at stake, there are some very real risks of attack.

I'd educate the people who will get the money. They get access to the safe deposits, and issue the transactions. With a multisig, there's no single point of failure, and with hardware wallets there's little risk of getting hacked.

Maybe I'm just not aware of all of the Opsec things that have been done to make Bitcoin transfer stupid simple, but I have instant goosebumps anytime someone claims they can do something in an operationally secure way, especially when 10 figures of currency are involved. At that point, you need to be training your protocol to be secure enough to survive the team from Ocean's 11 or the Russian government, not just script kiddies with too much time on their hands.