It doesn't really matter that there is any big difference or not; they're just nice sayings to have in your mind. They are straightforward questions to help you make wise reactions. You don't have to figure out the differences between a lot of these things.
One of the problems that many scholars have regarding Buddhism is that too often they think everything has to be separated into little compartments. Like with the Four Brahma Viharas, we have what we call Compassion/Lovingkindness, that's the first one. We then have Compassion as the second one. We have Sympathetic Joy as the third one. Equanimity as the fourth. The Pali words are: Metta, Karuna, Mudita, and Upekkha. A lot of scholars want to try to keep them separate, but no they're not, they overlap, they connect. So often, don't worry about individual things being definitive. Look in general at a lot of the stuff, grasp the meaning of it and go with that.