I have copied your code and will look at it later. But for starters, I think the syntax is incorrect on your src statements. You need a url option and the font name should be in single quotes:
As far as the syntax of the path to the font, I think you would need to include the font in the epub file itself, in order to get it over to the nook, right (just as image files are included in the the epub file itself). An epub file is really a zip archive which contains everything the ebook needs to do its thing. i do not think it can have any external files.
So, perhaps in Sigil you can add the ttf file to the epub file itself. Try to add the .ttf file to the font area of the epub file - it's at the bottom of the left panel in Sigil.
Then in the css file, for the path to the font, it must be relative to the css file I think that would be:
but I'm not sure. But try that idea. For sure, you need to put the font into the Font area of the epub file.