I think annotating each sentence with focus on one entity at a time makes the most sense here. Yeah, you'll be seeing the same text multiple times, but you're always focusing in a different span within the sentence, with potentially very different sentiments.
An alternative solution could be to add "options", make them multiple choice and create one per span + sentiment combination. So you'd have "very friendly": positive, "very friendly": neutral, ..., "successfully did the surgery": positive, and so on. And you could maybe use the "style" property on the choice options to assign different colors. But this still seems messier and means there's a lot more going on per task (and more potential for making mistakes).