"Spare" memoir to reveal royal family secrets.
Harry and William's altercation over Meghan is detailed.
Charles pleads with his sons not to make final years "miserable."
Harry and Meghan's Netflix show precedes the book release.
William and Kate also criticized in memoir.
Pulitzer Prize winner JR Moehringer ghostwrote the book.
"Spare" to be published on 10 January.
Harry wants a "family, not an institution."