During much of ROCH, the Mo Brothers were depicted as petty characters who bullied and held grudges against Yeung Gor during their youth, and were jealous of him (and each other) when it came to the pursuit of Gwok Fu's interest. Though they never became great heroes, they eventually matured into decent men who bravely assisted their teacher Gwok Jing and their father Mo 3 Tung to defend Seung Yeung Fortress from the Mongols. They even buried their hatchet with Yeung Gor.
Mo Sau Mun, the younger of the two Mo Brothers, had descendents who showed up in HSDS: Mo Lit and his daughter, Mo Ching Ying. This father/daughter combo was quite despicable. They thought nothing of manipulating and torturing Cheung Mo Gei to learn Tse Tsun and the Dragon Sabre's whereabouts, and Mo Ching Ying might have had a sadistic streak in her (she helped her cousin to beat up a helpless Cheung Mo Gei at one point out of pure malice). In short, Mo Lit and Mo Ching Ying were much worse than Mo Sau Mun had been, though he had hardly been a saint himself.
If Mo Sau Mun could have seen what his descendents had done, would he be ashamed of them, or do you think he might have tacitly approved...perhaps believing that in their position, he might have done the same thing?