It's very simple. You have to make a will with a lawyer.
If a lawyer violates the code of ethics, he is to be the first one can access your Million BTC for himself. you must be thinking to do not just giving up the seed to the lawyer. He is a human who has a mind and feels if gets stuck needs the money asap and doesn't know how to get it, your seed is very easy to access and immensely helps him.
Lawyers or banks are not as safe as we think, they also have greed and if it is a large amount of money they are willing to ignore morality to get it. I wonder what are we investing or making money for?, for whom? for ourselves or for our loved ones or families. If it's just ourselves, then we don't need to share or inherit it to anyone. And if we do everything for the family, instead of giving the private key to the lawyer, give it to the person we trust most in the family. It's strange how many people don't trust their loved ones but trust their lawyers.