Richard,
I see in the style sheet window that you have FOSI source edits.
Did you create these or have a 3rd party create them?
If it is a 3rd party, then you should contact them for assistance with your needs.
If you are using FOSI source edits, then you want the figure number counter created by the title element in the context of a figure.
That count would be put in a savetext variable that saves \Fig. \,$chapternumber,\-\,$figurenumber,\ \.
The _ufe:figureTitle would count the sheets, sheetcount. The after generated text for the _ufe:figureTitle would have a savetext variable that would saves \Sheet \,$sheetcount,\ of \,$totalsheetcount\
totalsheetcount and sheetcount are zeroed at every figure element
_ufe:figureTitle increments sheetcount
title in the context of figure increments the figurenumber