Willing your bitcoin assets with an involvement of a lawyer to me isn't a consent of third party yet because while you lives, your seed phrases is just between you and your trustee being your lawyer and when you're no more, the lawyer can sideline it and your family could be left with nothing and they literally can't fight it out because there's no proof that will.
The only option is having a private savings box that may contain your internet private details probably if you've your seed phrase stored online or stored offline in the box and during when you exit, behold, your wallets and privacies can be traced if your family can get reach to the box.
You only need to have a family that respects your Privacies and you too trying to be much logical so they you don't over trust them because anything anytime is possible to happen by any memeber if the family throwing stone to invade.
At some sensitive points in life is so choked that we'd be left with only one option and no other possible ways. That's he scenario here.
It think it all depend on the level of trust between one and their lawyer, there are still good trusted worthy lawyers that are genuine, and still carry out their duties according to the oath they took upon their call to bar, but lately the heart of men (man/woman) is becoming very deceitful, so it would be quite difficult to trust any lawyer with that currently.
Well, I agree with the idea of a saving box but to be specific not the regular local saving box but a safe that has a code in which you can safely store documents including the password which could be handed to your next of kin but not by your lawyer cause the lawyer may still send robbers to invade the house and penetrate the safe.
I don't even think such information concerning the safe should be entrusted to everyone in the family cause in every family there's always a bad sheep that would always kick family laws so it should be given to a trusted person who could either be your wife if you're married, next of kin or mother if the next of kin is still a child.