Yes they are related. Soleil used to live in Kasa-Vubu and Dede Djascko comes from Matete. Because of having difficulties of breaking through the music-scene in Kinshasa, he went to Brazzaville after that his friend Costeau Tshimpaka, who used to play in the same band like him (I think Limete), advised him to do so. Dede getting known in Brazzaville with Patrouille des Stars and Soleil getting known when he joined Quartier Latin. Dede started to get known in the Congo-Kin community when he collaborated with Fally in Droit Chemin (many people still think that his vocals are those of Soleil), he also worked previously with Karmapa in his two first albums (but the thing was that many didn't really knew his name and who did the vocals)