The family member part is addressed in the comic

Ok, let's try. This is fun!:

What currency is it based on? What if a country is experiencing inflation or they don’t use USD? What if their wealth is in crypto? Or painting? How does this Event know the worth of an artwork in real time?

For currency and threshold, it's a floating ratio. Find the ratio in 2026 of $1 billion USD to the median global household income. Then set the boom limit as that ratio moving forward, measured in a broad basket of currencies. (Probably with some time averaging to account for weird short-period market swings.)

For valuing assets, it's defined as fair-market value for whatever can actually be fairly valued. Stock, bonds, land, anything traded on an open market. For more subjective things like paintings, it's when you perform some action to take financial advantage of its value. So you buy it for some amount, take a loan out against it, sell it, etc.

What if their worth is based on their knowledge(Like semiconductor trade secrets)? What if they use that knowledge exchange for power?

Intellectual property is valued like paintings. You always are free to have whatever knowledge you want in your mind. But whenever you license that knowledge or financialize it, the value of that asset now counts towards your wealth. Again if you take out a loan against it, sell the license for cash, insure it, etc.

It won't do much for those using their knowledge for power. But people already do that through blackmail. Or if you're thinking scientific knowledge? Well, Professor Evil at UC Berkeley may be the world's foremost expert on making the world's best computer chips, without whose active participation the industry would nearly collapse...but we're not going to let Dr. Evil run the world just because he knows how to make the best computer chips. I think we would rather just get by with worse off computers than put up with that. And fundamentally, this isn't meant to correct all injustice in the world. Evil men could still be elected to great power. Wealth is just a uniquely fungible form of evil that makes it so dangerous.

What about the people who are in power, who control money but don’t own it? What if they exchange “vacations” instead of something tangible?

If you're just an ordinary politician working in good faith, merely acting as a steward of the people's money? You're fine. Are you a totalitarian despot whose personal and state bank accounts are legally or effectively one and the same? You go poof. If you try to use any legal chicanery to get around it, it knows. Magic in fiction often works on True Names. This magic can recognize True Owners. So no signing over your estate to a trust or "charity" that you control. If you retain control over any asset for your own financial benefit? It counts towards your boom limit. It can recognize a True Owner because MAGIC!!!

When a family member dies, does the money automatically go to the next successor? Is there a cooldown or instantaneous? Is there a maximum number of chain reactions?

I believe in most places you can disinherit all or a portion of your inheritance. Some people legitimately do not want to inherit anything from certain loved ones. Imagine you had a relative who you hated and you knew made money in an absolutely evil way, but you still ended up receiving a large sum from their inheritance. You might want to simply never receive that money.

The heirs post-poofing could simply sign away portions of their inheritance to other people or to truly independent charities.

What if the government is motivated by power, not money? What about the transitional period kills more poor people than the wealthy? Can you kill someone by a bunch of people donating?

Again, it won't prevent all the evils of the world. Just reduce some of them associated with the uniquely fungible threat of money. The transitional period very well may kill some people. But mostly that would be from civil wars in countries after their dictators go poof. Billionaires in most countries would not cause political breakdown or societal collapse. Even in the US, very few politicians are themselves billionaires. There aren't that many of these people. We can get along without them. In those countries that it does lead to civil war? Well, the death of a dictator is a chance. A chance for a people to start again. How they handle it from there is on them.

For murder-by-donation. I think that's extremely unlikely to work. Even today, any method of paying someone will have fraud protection limits in place. Try to shove a billion dollars in small donations through a Venmo account. Good luck with that.

And the classic one: What if they are piloting a plane with innocent passengers?

For situations where it is impossible to kill one person without directly killing other innocents, the poofing is withheld until that condition is removed. (Like when the plane lands.)

And no cheesing this! For example, maybe a dictator has a brilliant idea:

He'll order his scientists to connect a large bomb under a boarding school to a sensor that measures his heartbeat! Thus, he can never be poofed, as poofing him will kill innocents. Thus, he can amass as much wealth as he wants!

The dictator begins to type an email to one of his minions, to begin arranging the scheme...and he's poofed.

The curse/blessing is smart enough to recognize those trying to cheat it. The annals of history will be filled with stories of brilliant fools who thought they had found some clever way to trick the curse/blessing. But they forget. It can read minds. It can read hearts. It knows your intentions. It can do this, because it's MAGIC.

In practice, this is going to result in people maintaining wealth well under a billion dollars. This curse/blessing that has settled upon humanity is now effectively an out of control superintelligence ruling over us. We are being judged. We do not know the exact criteria we are being judged by. The only path to survival is to ensure that you are nowhere near the threshold of wealth needed for summary execution.