Other books about this?

Yes there was something titled "The Strange Case of the Cottingley Fairies" or similar - do a Google search. I've also read chapters in various books - Unexplained, Arthur C Clark etc.

'The Case of the Cottingley Fairies' by Joe Cooper
'Fairies: The Cottingley Photographs' by Edward Gardner

there is also a screenplay of the film itself with the same title, by Monica Kulling

Colin Wilson deals with this case in depth in his books, one I have on hand is his "The Mammoth Encyclopedia of the Unexplained". His chapter on the Cottlingley Fairies is very good and indepth. In fact, this film seems based on his relating of the events (with Francis seeing the Fairies but Elsie not). And his conclusions where that, while it was a fraud, the women kept saying that they saw something in their beck when they were young, and Colin Wilson believes them.