Regarding the final clash between Zhou Weiqing and Shangguan Tianyue, the first one had been real, the second one was not. Simply put, Zhou Weiqing had used the 'crying-face' hammer for the first hit, and the 'smiling-face' hammer for the second one. Shangguan Tianyue's dire injury had been mostly self-inflicted.
Shangguan Tianyue had told Zhou Weiqing beforehand that he wanted to decide how heavy his injury would be.
The reason Zhou Weiqing used his full strength when fighting Shangguan Tianyue was that he was worried Shangguan Tianyang might see through their foil, but also because he wanted to test his own strength. Since there was a willing Heavenly Emperor Tier powerhouse who had no harmful thoughts toward him, it was a good time to do so.
The truth is, the older the wiser. Even if they had been fighting for real, Shangguan Tianyang still saw through it, because of Shangguan Tianyue's performance at the end. He did not stop it, however.