There is no perfect solution to this, as the person must take a certain level of risk. It would have been lovely if such a person could keep the seed phrase all to himself, but eventualities and death may happen. Bank keeping is a good one, though expensive and you should never let them know it's the seed phrase, so keeping them in part is smart. A good law firm is another means to keep this, but like I said, in part, anyone can compromise.

All these troubles are because spouses, relatives, or anyone may compromise, yet they must be part of this. So, just as you entrusted a part to a bank/lawyer, you can entrust the other part to anyone you trust most in your family. That will be the person who would link the pieces together in case of an eventuality.