The Times has some excerpts from the book regarding the private secretaries.
https://www.thetimes.co.uk/article/...-secretary-fixed-sandringham-summit-mqh05mj6w
They reveal mean little nicknames Harry has assigned these three senior secretaries. Sir Edward Young is The Bee, Simon Case is The Fly and Sir Clive Alderton is The Wasp. There are some odious explanations for the names. I'm assuming these men had to sign NDAs.
Even if they haven't signed NDAs Sir Clive Alderton and Sir Edward Young are the King's Private Secretaries and so very unlikely to comment given the Boss has decided there will be no response. Simon Case is the current Cabinet Secretary and so, again, very unlikely to make any comment as that will drag the government into this mess.