1) Download the guide from the first post in this topic:
https://www.mobileread.com/forums/showthread.php?t=28447
2) SonyFont simplifies "Step One: Modifying our font" and extends it for the two other typefaces. Instead of downloading FontCreator and renaming the font in it, which is prone to mistakes and requires a commercial app, download SonyFont, choose the font file and let it do its work. Then you can continue with steps Two and the rest from the guide.