Thanks all for your responses! I've resolved all epub check errors. The font names were not respecting the correct case for folder/file name. However my character issue still remains. I've added some screen shots to help illustrate the problem...
One is the Sigil view. You can already see a rendering problem...
The second is the view in the Kindle previewer. You can see that those eff'd characters are rendering in a default font...
The third is a cap of the font characters/glyphs in the font manager. The characters do appear to exist in the font.
Thanks again for everyone's help!
EDIT: Removed attachments as they contained names of real people.
