Ye Jiushang ordered Little Lei to deal with the Electric Water Eels and Zhuri and Fuyun to deal with the vines because he wanted to focus on studying the Evil Bone Spectral Soldiers. After all, they were the most terrifying. The other two were nothing serious.
The spectral soldiers were not alive, so they would not die. The only reason they could move was because of their grievances and vengeful spirits.
If they could eliminate the root cause, wouldn't they be done with these Evil Bone Spectral Soldiers?
"Xin'er, do you remember the Soul Awakening Song I taught you previously?"
"I remember! Can the Soul Awakening Song deal with them?"
"The Soul Awakening Song is not enough, but if you add the Curse of Vengeance, it might do the trick."
"The Curse of Vengeance? Is that difficult to learn? The situation is critical now, and I might not make it."
