And then those law firms would hire one of these trusted third party escrows to directly handle the coins, assuming they have access to the private keys or the the locktime transaction sends it to them, multisig of course, but for simplicity maybe just the backing of law would do. If it were a 2-of-3 multisig and only 1 survives, no one gets the coins.
Yeah the law firm case is sort of "everyone is dead" so it doesn't really matter what happens to your money in this event anyways

But yeah you can have the law firm be multisig'd with a key known to all inheritors so they can't simply steal the funds.