If you think the book is about the inners of the British monarchy, you are sadly mistaken. Either you haven't read the book, or you live in the same delusional world as do people who think Black people benefitted from slavery.
Spare is about Harry's inner-perspective and his metaphorphisis. The relationships that are presented in the book are reflections that show Harry, the good, bad and the ugly. The memoir is a journey with a climax at the point of real therapy.
We should commend Harry for his great awakening. It takes courage to act on faith and leave toxic relationships (family or not) behind.