Thank you, Kate. Got the fonts and have looked them over. There is one very minor error in one of the fonts, and even that depends on how you want to look at it. But it's not enough to make any real difference.
Since I couldn't find any notable errors with the build of the fonts, I then simply tried them with a bunch of apps. Photoshop, TextEdit, SoftMaker Office, VivaDesigner and a few others. All of them had access to all of the fonts.
Proof in hand that the fonts behave as I would expect them to, I then opened PhotoScape X. It's not just you. This app does a terrible job accessing fonts. I could choose SP Blunt Outline and Script, but not Regular or Italic. For the other, I could access Vintage Forge Regular, but not Condensed or Script.
In short, there's nothing you can do other than send a message to the author of PhotoScape X and let them know they need to fix their code for font handling.