I too was swept away in the "lovely old man walks around his garden for the NHS" sentiment until his whole family accompanied him to I believe it was The Bahamas, or somewhere in the Caribbean because, they said, he's always wanted to go there.
Hmm - I always thought it was an odd place to have always wanted to go to and tbh, the thought of the flight and all the aggravation that goes with long haul travel these days would put me off going, let alone someone 30 odd years older.
The book presumably, was ghost written and I would hazard a guess, very loosely based on a few interviews and embellished for sensationalism.
Was he in cahoots with the daughter? Well, we'll never know. I'm not sure at that age I would be bothered to go through all that relentless publicity and intrusion to make money. None of us live forever, when did he think he was going to spend it? Unless, I suppose, he was happy to use it as an opportunity to to increase the inheritance.