@Jedidiah "How do I make Librerator pull up all the fonts from a family?"
I have also been experimenting with better fonts for epubs and have seen the same treatment of the font families. I have also used the PT_Serif and NotoSerif with very good results. I have found the epub correctly selects the regular, italic and bold fonts automatically as intended by the author when just the family is selected from the font menu. I don't think there is a way to select just the bold or italic for the base font when only the family is presented as a choice. Is that your interest?
The DroidSerif font is a very nice font and can be found here:
google.com/webfonts/specimen/Droid+Serif
Click the download 'down arrow' to get the TTF files in a ZIP.
@sk8terek
I have just started using KPV and unless the crengine in Liberator is slightly different then the bolds and italics are already displayed correctly if the font families are available. Have you tried adding your own font families like the Noto family? I imagine the crengine in Liberator might build its own italics and bolds if those were not available except I haven't tried everything and would want to avoid that need so prefer using complete font families.