I don’t agree with not helping family members with medical expenses when you can, and yes your FIL was obnoxious, but I don’t agree that children ought to feel entitled to an inheritance.
There was a time when a child’s ability to make it in the world was tied to acquiring land, which in the upper classes was handed down from generation to generation. It went to the first born, however, because otherwise the family “opportunity” would be diluted so much in a very few generations that there would be too little land left to any particular heir to make a go of it. That was how the older generation handed down opportunity from one generation to the next. In lower classes and for younger siblings of the wealthy, it was an education or a trade or a craft that was handed on, not money. (The truth is, it was more that the children were expected to feed their parents in their old age when they could not work!)
I very much doubt that this wealthy couple is going to deny their children any educational opportunity to make their own way. Where introductions are needed, I do not doubt that introductions will be made, too. I also doubt that they’re going to watch their children or grandchildren go without health care while they still live.
I still don’t see why anyone should expect to inherit more than a very modest portion of four billion dollars. Who needs that much? No one does!! The parents see their amassed wealth as something far beyond the needs of both themselves and their heirs, and therefore something that ought to be used to benefit a greater number of people, starting right now. They aren’t going through the wealth to please themselves, but in order to do philanthropy both now and after they die. That is a totally different and very much richer legacy than your obnoxious FIL was proposing to leave behind him.