In historic records, there were several Emperor-consorts Caos in the Song Empire, but only one became empress: Cishengguangxian Empress (慈聖光獻皇后 ci2 sheng4 guang1 xian4 huang2 hou4) (1015 - 1079), the wife of the fourth Song emperor, Renzong (仁宗), none of whose children became an emperor.
However, this therefore does not render the historical existence of the "Royal Uncle Cao" impossible. Because in pre-modern China, the address "uncle" also meant "brother-in-law". Sometimes specified as "Wife-uncle" (妻舅) or as a respect, "Uncle zi" (舅子) (parallel to Lao Zi). Cishengguangxian Empress did have a younger brother named Cao Yi in historical record. But the given name of Royal Uncle Cao being Yi as well could be a post hoc.
Cao Guojiu's younger brother Cao Jingzhi (曹景植 cao2 jing3 zhi2) was a bully, but no-one dared prosecuted him because of relation to the queen, not even after he killed a person. Royal Uncle Cao was so overwhelmed by sadness and shame that he resigned his office and left home.