I’m sorry but I’m not sure that I follow all of your comments/questions. High level, royalties are owed on Products (unless a royalty-exclusion applies). And use of UE4 to create a video game means that Product is royalty bearing.
I’m not familiar with what you call choose your own adventure YouTube. Normally speaking, there is no royalty on Products which are linear video (the normal content on YouTube). It’s an interesting question if there is some kind of semi-interactive video content.