Hello Andy,
Good to hear from you!
My route to your great - uncles: James and Herbert Buck is a bit complicated. You and I aren't related, by the way.
My wife's brother, Patrick, is married to Carmel. Her uncle, Peter Broadbent is the nephew of Rene Broadbent, who married James Buck.
I was helping Peter with his Family Tree and found references to James in a couple of books on the Battle Of Britain. By chance I then found reference to Herbert and his death in a flying accident in April 1945, towards the end of WW2.
I believe their father was a minister in The Catholic Apostolic Church.
That's about as far as I've reached, so I'd be more than happy to share any information.
Cheers
Clive