The first question is, why didn’t Sister Shi help
It's very simple. Shiki had fought at Shirou's house first, and then she was running for her life. She had very little energy left. She didn't know the details of Waver and others, and it was not easy to act rashly with Mina and Mizutsu Ayako as the two burdens. It would be OK if Shinji came, but Shinji played with fireballs and smashed the treasures, which directly eliminated the possibility of Shiki intervening - Shiki's body was fragile, and she would die if she was not careful, and died from AOE - Shiki was cute, but she was not stupid.
The second problem is that Gray and Iskander can’t hold anyone back.
This is really unstoppable. Let's talk about Gray first. Gray is about 15 years old. She has been living in the cemetery before. She has little experience in exorcism. Although she has the physical fitness of a servant enhanced by Yade, Araya's body is also inhuman (dodge bullets, crush skulls with bare hands), not to mention that he has become much stronger after resurrection. If it weren't for the mysterious suppression of the Holy Lance, which invalidated Araya's barrier, Gray would have died. As for releasing the Holy Lance, this is very troublesome. It needs to be charged in advance, and there is no chance.
Next, let's talk about Iskandar. This is not Iskandar's problem. The main reason is that Nero Chaos's characteristics are too troublesome. He is basically a weakened version of Tima. Not only does he have 666 minions and 666 lives, but he also has an advantage over Tima. He can turn himself into black mud. How can the emperor delay? Unless he mobilizes the royal army. The problem is that the emperor has not seen through Nero Chaos's true colors, so he can't just reveal his trump card.
By the way, even if the King's Army was opened, the Emperor might not win? Why? Because to kill Nero Chaos, he must kill 666 of his lives (seeds of life) at once, and the Emperor does not have such means. Even if he turns into black mud, you may not be able to kill even one. If he wants to win, it can only be based on the sun (mental world) in the King's Army being effective against the Dead Apostles, or the priest group of Amon under the Emperor's command having a way to restrain the Dead Apostles.
Some readers may not agree, thinking that the traitor praises Tsukihime and the Death Apostles too much. In fact, it is not true. The twenty-seven ancestors are all monsters comparable to high-level fantasy species. The lower limit is a servant with average attributes and average treasures, and the upper limit is even greater than the gap between the worst servant and the crown. After all, there are three-story pyramid residents like Primate Killer and Mercury U.0 who can definitely not be dealt with by one crown, and multiple crowns may not be able to deal with them. And Mushroom also said that the twenty-seven ancestors also have the difference between upper and lower positions. The upper ones are much stronger than the lower ones. Nero Chaos belongs to the upper position. His characteristic is that he can withstand beatings. To some extent, he can withstand beatings even more than Elquit! If it weren't for the plot killing or the compatibility killing, I don't know how he died. He is currently the most buggy one in the behind-the-scenes troublemaking group except for Grandpa.
Finally, please remember that this is the troublemaker group that has been involved in all five wars. They are the big villains. Don’t underestimate them.