Bob,
The Kenton arrangements - a great wodge of them as I have seen them with my own eyes - were given to Brian by Stan in the early 1960s during one of Stan's visits to Brum. The story of how this came about used to be on Brian's website, but alas that website is no more and there is just a rather dormant Facebook page with very little content. I don't have any contact details for Brian at all.
A lot of the jazz musicians made the bulk of their living from the large orchestras and session work, and the advent of sampling and people like Hans Zimmer have killed off all the music work in the film studios. Covid has put the final nail in the coffin, not that any of the guys you mentioned have been around for ten or more years.
John,
Humph had a darned good band on the few occasions that I went so see him, and he was a gentleman, no doubt about that.
Maurice