Even with a tutor and years of practice it was virtually impossible that Peng Yong would have been able to speak English well enough to communicate as well as shown with William Garin. English is a phonetic language with completely different sentence structures and grammar than tonal Chinese.
The film , however, has Peng not only understand spoken English but also idioms and nuances. This would be difficult for many native English speakers and it would nearly impossible for a older learner to do so.
Only one magnetic stone, which can pacify the Taotie, appeared in the movie. The stone was brought in by William the European mercenary. In reality, Chinese civilization first made compasses from magnetic stones in Han dynasty (< AD100). By the time point of the movie (somewhen between AD960 and AD1127), the compass had been widely used in navigation. It shouldn't be hard to find more magnetic stones inside China.
The "drone" Tao Tei's eye placement does not conduce to its position in the horde. As a protector and hunter for the queen, it would need the predator's forward facing eyes, rather than side eye placement, to allow for binocular or stereoscopic vision. This would allow the monster to see and judge depth especially during the great-height wall battles against the Nameless Order. Predators need this depth perception to track and pursue prey. Its current design suggests that IT could be the prey.
It is shown that all the Tao Tei froze when the queen died. But if they were all connected to her for the whole time she would not have to send orders to them explicitly. The queen is depicted more like a general sending orders to her army (and then the army obeys - seemingly independent from her) than a brain to an organism like it would be concluded from their freezing when she died.
When we're first seeing Lin Mae jumping off of the wall to fight, during her jump in which she has a spear in each hand and does a back-flip, one of the spears can be seen phasing through the rope when the two should have collided.