Xiao Xiao definitely had not come as a representative of the Endless Fire Territory.
The relationship between Lu Yuan and Xiao Yan was rather complicated.
From Yao Lao's perspective,
Xiao Yan was Lu Yuan's Senior Brother.
From Nalan Yanran's perspective, since Lu Yuan was Nalan Yanran's Senior Brother, and Nalan Yanran had ultimately gotten together with Xiao Yan after who knew how many Three-Year Agreements, Lu Yuan was also Xiao Yan's Senior Brother by seniority. Although that status was outdated, the Yun Lan Sect always had certain special methods—such as forcibly elevating Lu Yuan's seniority.
For example,
to prevent Lu Yuan from bearing the charge of dishonoring his Master and ancestors,
Yun Shan had specifically pulled a slot from among his fellow disciples.
Though all of Yun Shan's fellow disciples were dead.
Yun Shan had at least been a Dou Zong.
Of course, he was now a Supreme.
However, since they were calculating seniority, they certainly could not use current cultivation levels. They had to calculate based on objective factors from back then, such as age and background. For instance, Yun Shan's Master was dead, so his fellow disciples had naturally all died of old age as well. Though Yun Shan had no direct Senior Brothers or Junior Brothers—he himself had been the Yun Lan Sect's Senior Brother, Young Sect Leader, Sect Leader, and so on, remaining alone from youth to old age and even now—his Master had fellow disciples, and those fellow disciples had disciples of their own. In other words, they were the disciples of Yun Shan's Martial Uncles or Martial Uncles Senior.
Naturally, those disciples were Yun Shan's peers.
As for Yun Ling...
Strictly speaking, he was of the same generation as Yun Yun...
He was also the disciple taken in by one of Yun Shan's Junior