The Web fonts are not applied within the frame of the inline frame of IE9 and later versions.

Web fonts are not applied inside inline frame (<iframe>) tags in IE9 or above.

When using inline frames, you need a TypeSquare-specifc tag not only for the page inside the frame (the child page) but also the parent page. In addition to the child page, the font family being used must also be applied to the <iframe> tag in the parent page.