Thank you for writing in, first please update your X and Cornerstone to latest versions because what you have right now is not compatible. Please refer here for the latest versions supported.
Remember to clear all caches after updating so that the code from the latest release is always in use. This will help you to avoid any potential errors.
After you have setup your Templates > Fonts, navigate to Theme Options > Typography enable the FONT MANAGER, and look for BODY FONT and HEADINGS FONT option.
Hope it helps,