In ancient times, parents had much more direct control over whom their kids married...almost *absolute* control, even.
Hui Juk married the Hsi-Hsia princess in DGSD. I'm surprised it happened so smoothly. There was no objection from the Hsi-Hsia king? Hui Juk was 1). a foreigner (a Han Chinese as opposed to a Tangut), 2). a former monk, and 3). a commoner. Somehow, the Hsi-Hsia king was willing to overlook all of these things?
I guess it's no more improbable than Genghis Khan permitting Princess Hua Jeng to marry Gwok Jing, but at least Gwok Jing impressed the Khan with this character and his prowess. Maybe Hui Juk did the same for the Hsi-Hsia king?