Bitcoin Inheritance Software

For me, Bitcoin is essentially feature complete. I can buy and take custody of a scarce property that no one can confiscate or debase.

The only part that doesn’t sit well with me right now is inheritance. I don’t want my savings to be lost if I die unexpectedly.

Does anyone feel like they’ve found a service or strategy that solves this problem?

I do not want to give anyone custody of the keys for my holdings. Many strategies that I’ve seen involve sharing your key in some way or using a 2 of 3 key. This doesn’t appeal to me because it makes it possible for someone else to transfer your bitcoin before you die (even if everyone is an honest actor, it could end up in the wrong hands out of incompetence). The ideal solution should not involve sharing any active keys (active meaning keys for an address with non-zero bitcoin balance).

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If there’s no existing service, I’m considering trying to build something myself. I’m thinking of something roughly like this:

1. Each person you want in your inheritance needs to have their own address that they share with you. How they manage their keys is up to them. (Or you could set them up yourself and share with them)
2. You create a time locked signed transaction that distributes your btc among the heirs. The transaction is only valid in, say, 3 years. You can share this transaction with a few people in the will, or some people you choose as executors.
3. Once a year, you send your bitcoin to a new address(es), thereby making the old inheritance transaction useless. Then you repeat step 2 with the new address(es).

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Some of the cons I can think of:

1. Very manual, requires lots of work, don’t want to have to manually do this every year or two.
2. Requires inheritors to do work beforehand (benefit of potentially getting them interested in Bitcoin)
3. Any BTC you save between the issuing of these inheritance transactions will be lost.
4. Shares with heirs how much BTC they would receive if you die
5. If an heir dies in an accident with you that share of Bitcoin is lost unless someone else can access their keys.
6. You need to transfer btc every year and incur the transaction cost of doing that.

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Some of the pros:

1. Never trusting anyone else with custody of your Bitcoin
2. Each person is responsible for their own keys
3. No 3rd party trust (outside of executors, but executors could be every single heir in which case the only trust is on the heirs to broadcast the transaction if you die, which is in their benefit)

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Some questions:

1. Is it possible for a signed transaction to be somehow based on percent of btc at an address, instead of fixed amount? This would be helpful for keeping the inheritance transaction valid even when you save more bitcoin.
2. Is it possible to invalidate the signed transaction without sending all the btc to a new address?
3. Is there any good existing software for building these kinds of custom transactions, for experimenting with what's possible?
4. Does this sound like something worth building?

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Any feedback is welcome. Thanks!