As for how many Tribulation Body Realm experts the Two Vassals have in total, Xia Hong certainly doesn't know.
But having personally ventured into both places, he can somewhat estimate.
Take Chen Cang for instance, on the surface, apart from Landgrave Chu Longteng, Commander Chen Liwu, former Grand Master Chen Lixin, then the Five County Governors, Two City Lords, Red Dragon Army Admiral Wu Dongyang, and the four department chiefs in military, justice, jurisdiction, and civil affairs: Chu Tianba, He Taiping, Wang Xuansun, and Chen Tianshuang. Finally, the two army commanders of Red Dragon and White Robe, Wu Dongyang and Chen Tianqing.
This makes a total of sixteen.
Of course, this is just on the surface. The Great Xia capital always knows to keep some cards up their sleeves; with Chen Cang's three-hundred-year heritage, how could they possibly lay all their cards on the table for others to see?
