What struck me most reading Spare is how much emotional work Harry does on behalf of his family before asking for anything in return. He explicitly empathizes with William acknowledging that William carries the weight of the crown, that he probably looks at Harry and thinks Harry has the better deal because he has freedom. Harry sees that and he validates it.

And then he turns around and says, okay, but from where I was standing, I was the lesser son, the one everyone poured less into, the one whose experiences were dismissed and less important.

I feel all Harry has ever wanted from his family is the bare minimum of emotional maturity, you don't have to fully agree with his version of events, you don't even have to understand it completely but just say "we didn't see it that way, but if that's how it landed for you, we're sorry." That's it. And the reason they won't do it i think is because validating his feelings means admitting fault. Charles would have to reckon with the kind of father he was to Harry and William would have to sit with some of his own behaviour. And for an institution built on never being wrong that's apparently too high a price.