Overlays usually come as static *.jpg image or as a link to a browser page, which in OBS you either include as media source (image) or as browser source. Display capture is a last resort, if game capture and window capture don't work. However, you capture games with game capture, not with display capture. One display capture already grabs everything that is on the display.

It's not clear how you need multiple display captures just to add overlays.