Sarima's two sons are kind of jerks. Manek especially is a serial killer in the making. He cruelly tortures Liir, and we can't help but feeling relieved when he's killed.
After nearly killing his half-brother Liir, it stands to reason that Elphaba would seek revenge. Manek crucially serves as a milestone on her path to Wicked Witchiness. She kills here without remorse. The scene also reveals how cut-off she is from her own emotions – she tells herself that she killed Manek because he was a bully. Her personal relationship with Liir didn't even enter into the situation at all, which seems a little suspect.
Irji is the kid we know the least about, though it's implied he's interested in religion and is probably gay (188.8.131.52). Irji's death is particularly gruesome and reveals the depths of the Wizard's cruelty.
Nor, the only daughter, is the most heavily featured, which makes sense in a book that places a huge emphasis on female characters. Nor is a younger version of Elphaba in some ways, but she's also another version of Dorothy. (Or, more accurately, Dorothy is another version of Nor.)
Nor is interested in magic and is also experiencing a sexual awakening in the novel. She helps to establish links between the themes of sorcery and gender/sexuality, which are also explored in the discourse on the Kumbric Witch. Fittingly, Nor herself enjoys stories about Witches (more on that shortly) and grows up in the land where Kumbric Witch legends are most prevalent. Nor's fate is one of the cruelest in the book; it seems that she's gone insane by the time Elphaba finds her (but fails to rescue her).
Just so we don't end on a sad note here, we'd like to look at a recurring scene between Sarima and Nor, who emphasize the book's interest in mothers and daughters. Two sets of mothers and daughters parallel each another: Melena and Elphaba (see Melena's "Character Analysis" for more on this) and Sarima and Nor in terms of their ultimate fates. But their bonding scenes are very significant.
"And there the wicked old Witch stayed, for a good long time."
"Did she ever come out?" recited Nor, eyes gleaming with the fun of the ritual.
"Not yet," answered Sarima, and leaned forward, pretending to bite Nor on the neck. Nor squealed and jiggled herself away, and ran to rejoin the boys. (184.108.40.206-57)
In a way, the mother and daughter are telling and retelling Elphaba's story; Elphaba is like the Witch who "came back out" and then disappeared again. This actually ties into the Saint Aelphaba myth as well and suggests that Elphaba is living out a story of "evil" that's been told countless times before and will be told again in the future.