Complex sentence: Corpang appears and says this is because Threal is not Faceny's world, but Thire's, Thire being, together with Faceny and Amfuse, the authors of three worlds of existence, relation and feeling.
Split into simpler sentences: Corpang appears and says this is because Threal is not Faceny's world, but Thire's. Thire, Faceny, and Amfuse are the creators of three worlds of existence, relation and feeling.