The only way to do this is by sharing your private key with someone very trusted or just storing it somewhere secure and keeping it locked until the time comes. The way to retrieve your valuables from the lock/vault can be specified on your will. Maybe be use a bank value to store your private keys on the paper wallet. Two parts on two different banks? That way there is lower chance of your keys getting compromised. And I am sure there are other people that have found out better ways to giveaway your wealth to your heirs. Maybe a quick google might help.
or if you have 2 heirs then best to have them both half of the key? so if ever that you died in accident or even in natural death , then they can just share each other and then boom , take the funds out?
though My wife and my children have idea what is crypto and yes i have split the keys to them 3 , (but of course I have my own funds inside my pocket) so if ever this happens then they can take it out without any issue.
You raise some good points about various ways to attempt to accomplish the extent to which any of us might want to give full power to someone and then to leave it up to that someone to engage in good practices, whether it is to follow instructions or perhaps even to have proper back ups of their keys that might be necessary for the other, and one of the possible remedies for a negligent or sloppy person might be to exercise 2 out of 3, but even 2 out of 3 might not resolve some situations in which one of the people who is irresponsible does their irresponsibility, and then one of the responsible ones ends up having a real and legitimate problem that even ended up screwing up their backup, and then in that case getting left with only 1 out of 3 ends up being the same as having nothing, since one of the other keys would still be needed.
Oh and your example of giving full access to the spouse, and perhaps it could be like a joint account and there is enough to completely cover everyone and you use it on a regular basis, and there are supposed to be restrictions on spending from the account up to a certain amount per month... let's say $3k per month or something like that (and presume the funds are in the ballpark of $1 million
**).. but then if you have your own separate $1 million, then you are still able to cope if your spouse runs off with the funds (or spends beyond the budget), even though that was not supposed to happen, and you did not authorize the spouse to engage in that kind of conduct, you have protected yourself by having right around an equal fund that you keep separate for yourself, just in case.
**Don't get me wrong. I am not trying to make these numbers untouchable, but I am trying to give an example of a fund reaching a kind of self-perpetuating status, and if the fund had only $300k in it, then the example would still work as long at the income being drawn from the fund is $1k per month, and of course, if there is money flowing into the fund on a regular basis, then the extra cashflow into the fund would increase the amount that can be drawn out.. and if the fund is still in its building stage, then maybe no money would be spent from the principle, and it would just be a fund with extra money, and ONLY the cashflow would be part of the regular monthly budget.