Hi,
The way that UI works, the blue boxes with gold frames are part of the main Dialogue Panel, so they're always visible. The NPC and PC Subtitle Panels don't control them.
Can you switch to the "Standard UI Prefabs / Templates / JRPG" version? It has an almost identical layout. The standard UIs are a lot easier to customize. It uses gray box images, but you can just assign the same blue-and-gold images that the Unity UI Dialogue UI version uses.
If you can't, then try copying the Dialogue Panel GameObject twice so you have 3 copies. Rename the first "NPC Subtitle Panel", the second "PC Subtitle Panel", and the third "Response Panel". In the Unity UI Dialogue UI component, reassign the UI elements for each section (NPC, PC, and response menu). Delete the unused elements, such as the leftover response menu stuff in the NPC Subtitle Panel and PC Subtitle Panel. Here's an example exported from Unity 2018.3:
CustomizedJRPGUnityUI_2019-05-06.unitypackage