The amount of responsibilities towards Harry, that his fans place on William because he's 2 years older, is extraordinary. They always forget he was just a child too.
Charles is a softy, and no doubt does feel a lot of guilt towards Harry - which he should do, frankly, although Harry also needs to grow the hell up.
William probably feels he owes nothing to Harry, having done his best to be a decent brother, but not wanting to be his brother's keeper his whole life. And if there was any residual guilt as the older brother and heir, that's going to be shot to shit now. Harry, both directly and through Scobie, has vilified his brother, Catherine (who was like his sister) and even had pot shots at their children.
I do think the door is still ajar between Charles and Harry. But William and Harry? I can't see it now, not after this book. Maybe in about 10 years if there's no further shite being lobbed from Montecito, but not in the short term.