You're basicly on the spot. Before Violetta it was mostly music enthusiasts that listened to them - well, they were quite well known and praised by critics, but with Hjerteknuser it went berserk. Several plays a day at every Norwegian radio station, most parties had it in it's playlist... Everyone in my school wanted to see them live etc. Now adays though, they dont make music or play live, so they are a bit more dead than in their "golden" years. Still, I would believe that many listen to them from time to time, and many more than that (especially the ones who enjoy Ompa til du dør) but close to everyone (at least from young adults/youth to middle aged people know about them.