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.
I think the seed needs to be split to the lawyer and the people you are going to give the funds in case of drying , with this I'm sure there is no one that can take the funds unless they will agreed to each others claim.
giving it completely to the lawyer will surely take the business effect as greediness may take place .
What if the lawyer doesn't want to give the rest or he knows it's too big, he will demand a bigger ransom. Once their work ethic is overshadowed by money, they can do anything. One more thing, we always prioritize privacy and will making will ensure our privacy and crypto assets? In my opinion, there is no need for outsiders to interfere in this matter, give it all to the people you trust most in your family. The people you want will inherit your property when you die.