When I was first shown them, I assumed that they were a single leaf: to judge by the widths of the borders, the text is on a recto, and the full-page miniature is on a verso.
The text and image clearly go together to form an illustrated suffrage to All Saints, but this back-to-back arrangement would be unusual for two reasons: first because one expects a miniature on a verso to have the text relevant text on a facing recto, and second because one expects a full-page Flemish miniature like this to be painted on an inserted single leaf, blank on the recto.
The blue velvet of the frame in which they are encased is fairly worn and looks old, probably Victorian. If so, this demonstrates that the leaves are not from a book that has been broken-up recently.
I was allowed carefully to open the frame, and it was only when I did so that I had some big surprises: first, as noted above, the "leaf" is in fact two leaves, framed back-to-back so that they appear to be a single one. Second, the backing-paper on which the miniatures are mounted are stuck to the two halves of the frame using pieces of old newspaper, and remarkably, it is possible to identify the very newspaper pages from which these pieces were cut.
I was able to make the identification simply by Googling a phrase or two, such as this fragment:
complete newspaper on the website of the National Library of Australia:
Of these, only Nicholson and Hackett are at all likely to have owned a medieval manuscript or miniature as early as 1886, and none of their manuscripts now in Australia can be shown to have been owned by them at such an early date (although some were demonstrably acquired at later dates). This means that no other manuscript can be proven to have been in Australia as early as the Flemish illuminated leaves described above. And even if not the earliest to be in Australia, these leaves are surely the finest examples of Flemish illumination to have been owned in Australia prior to the purchase by Kerry Stokes in 2014 of the Rothschild Prayerbook.