these 3 human species a myth?

The extinction of the reptilian dinosaurs some 66 million years ago, was a blessing to mankind, as they would have been the greatest threat to the continued evolution of mankind from our ancestors ‘The Mammals,’ of which our oldest known primate-like mammal ancestors, were the Plesiadapis, which came from North America; or the Archicebus, which came from China, or any of the other similar basal primates, which were widespread in Eurasia and Africa during the tropical conditions of the Paleocene and Eocene geological Epochs. And the evolutionary history of those primates can be traced back 65 million years, shortly after the time when the dinosaurs became extinct.

From which if those species did the Denisovans evolve and from which did the Neanderthals evolve and from which did the modern humans of today evolve??

Your problem is that that's not the definition of species. A species is the smallest group of organisms that share a common ancestor and can be reliably identified by unique traits not found in other groups.