I have played with your images and there is many reasons why they don't stitch well or even at all.
Firstly: Your images are shot in Aperture Priority mode. They vary in shutter speed and thus you get different exposures. You should be shooting in (M) manual mode and keeping the same Aperture and Shutter Speed for "all" images in the panorama set. You should also have a fixed White Balance and ISO setting. You must think of the complete panorama as (1) photo.
Secondly: Your images are somewhat out of focus and lacking defined features for stitching (especially the Nadir image). Again, these should be shot in a fully manual way. The lens must be fixed with no Autofocus enabled.
Thirdly: Your images are tilted I.E: not in the correct orientation. You must disable the "auto rotation" within your camera menu.
Lastly: You haven't shot enough images to cover the complete sphere. Meaning there are "holes" in your panorama. As shown in this sample.
Anyway, I hope this helps your in your panoramic journey.