Yeung Teet Sum was ostensibly a descendant of the famous Yeung clan of generals, who some 200 years before YTS's time, during the heyday of the Northern Sung Dynasty, fought against the Khitan Liao Empire. During the time of the Yeung Family Corps legends, the Yeungs were evidently aristocrats, with wealth and privilege that bespoke their importance in the Sung military. Closer to YTS's own time, his great-grandfather Yeung Tsoi Hing served under General Ngok Fei against the Jurchen Jin Empire.
By YTS's generation, however, the Yeung Family seemed to have fallen upon hard times. When Yeung Teet Sum was first introduced at the beginning of LOCH, he was a peasant farmer, and he and his wife had just enough to get by. In terms of fighting the Jin Empire, did YTS do that with only his sworn brother Gwok Siu Teen? YTS did not seem to have any siblings. I remember YTS and GST considering joining up with the Sung military after their children were born, but wouldn't it be a waste for heroes of their pedigree and skill to serve as standard infantrymen in the Southern Sung army? YTS was the descendant of Sung war heroes from an earlier era in the dynasty's history, after all, and his skills, though weak compared to the elites of wulin, were easily superior to those of a dozen or more ordinary soldiers.