Eren had killed three rankers in total by the time the stun effect on Oliver's forces was over.
Eren's wrath creature managed to injure two rankers in the next two seconds before the rankers were able to respond to the attacks launched at them.
The two rankers that were injured by the wrath creature were also affected by the wrath mana. It was just that neither they nor their fellow rankers were aware of what was happening to them. This is why they suddenly started hating the situation they were in.
Between the butcher and the fake butcher, Oliver immediately understood who was more dangerous. He intercepted Eren after he managed to get out of the stun effect. By doing so, he prevented the butcher from killing any more rankers from his side.
Ivor had also killed three rankers so far. Unlike Eren who was very handsy with his approach, Osan Junior preferred to use his spells and his daggers. Plus, by the time Oliver kept Eren busy, Ivor was able to catch up with Eren.