If they discovered that quite a few people on Ling Tian's side had broken through to the Quasi-Saint Ninth Order, Chi Xue and the others would certainly make their move—especially since none of the God Devouring Bodies among them had broken through. If that happened, the pressure on Ling Tian and his companions would increase greatly. Most likely, they would be unable to withstand both factions, and Fengyun Realm would be destroyed. After all, Ling Tian and the others weren't even entirely confident they could stop the Outer Realm Demon Race cultivators alone, let alone with Chi Xue's side joining the fight.
The outcome of facing the Outer Realm Demon Race cultivators alone was completely different from facing both them and Chi Xue's faction. If Chi Xue and the others attacked, Ling Tian's group would have to divert some of their forces to stop them. Otherwise, Chi Xue's side could easily destroy the temporary base and Teleportation Formations Ling Tian's group had established. Once they split off part of their strength, they would inflict far less damage on the Outer Realm Demon Race cultivators—especially if they had to deploy a large force to deal with Chi Xue's faction.
Chi Xue's side was also very powerful, especially since they had at least as many enormous Universe Flying Saucers as the Outer Realm Demon Race cultivators. Ling Tian's group would have to commit most of their forces to fight them, which meant they would have far fewer people left to deal with the Outer Realm Demon Race cultivators. Ling Tian's group could barely inflict any significant losses on them as it was, let alone after sending many cultivators to deal with Chi Xue's side.
That was exactly why it was so important to keep Hua Min'er and the others' Quasi-Saint Ninth Order