Wallace's group had just arrived at this place when they had seen that their target was already waiting for them in the middle of that main avenue of the Yellow City.
At that moment, Minos was already standing in that place next to the two specialists sent by the Hayes family to help him perform this scheme.
Since Minos had watchers from the Black Plain in this city, he already knew when these 'guests' would arrive. As such, he was already waiting for Wallace's group while having a smile on his face.
And when those members of the Chambers family saw this from the skies where they had come from, they soon understood the situation and didn't bother to try to attack Minos by surprise.
Their target had already made his plans. So, it would be better for them to act cautiously, together, without risking too much by going after Minos individually.