Xiankai is the father of Xing Yan and Zhifeng, so Wansha is the aunt of Xing Yan and Zhifeng. Although Guan Sha is 90 years old and Xing Yan and Zhi Feng are only two or three years old, Guan Sha is also their aunt.
You got it? This is about seniority. For example, when I go back to my hometown, people in their sixties and seventies still call me grandpa and bodhi old zu.