When you think about it, Kiu Fung and Hui Juk's deep friendship and sworn brotherhood was pretty implausible. Consider the events surrounding their first meeting: could their relationship have gotten off to a worse start?
On the day that Kiu Fung and Hui Juk first met (before they had been formally introduced to one another, in fact), Kiu Fung learned that Hui Juk's father had been a part of the plot that killed Kiu Fung's mother (and had been part of the subsequent coverup that had led Kiu Fung to even more suffering, including the death of Ah Chu). Naturally, Kiu Fung couldn't bring himself to forgive Hui Juk's father for what he had done. In DGSD '81 (and I'd be surprised if this were not in the novel as well), Hui Juk actually begged Kiu Fung to forgive the disgraced Chief Abbot of Shaolin, to which Kiu Fung regretfully replied, "I'm sorry, but do you understand how the events at the Gate of Ah Mun affected my life?" Hui Juk's father was subsequently beaten to death per Shaolin regulations (well, the beating was per regulations; the "to death" part was incidental) for his transgressions.
Kiu Fung and Hui Juk were both great men. I don't put it beyond them to not blame each other for their respective fathers' transgressions. Nevertheless, Kiu Fung and Hui Juk were both human. Somewhere in the back of Kiu Fung's mind, he should have had a difficult time looking at Hui Juk and not thinking, "this guy's father helped murder my mother and ruin my life." At the same time, how could Hui Juk not look at Kiu Fung and not think, "although my father did wrong and deserved punishment, this man would not forgive him even though I begged him." Maybe Kiu Fung and Hui Juk were great enough men that they wouldn't decide to seek bloody vengeance on each other, but to become great friends and sworn brothers? That seemed to be a stretch. Considering all the bad blood between their fathers, how could they even stand to hang around with each other? Seeing each other must have brought up bad memories. Even if they didn't hate each other, it's hard to imagine them enjoying each other's company enough to become friends, let alone sworn brothers.