In Akata Witch, Orlu (the Cynic), Sasha (the Apathetic), and Sunny and Chichi switch between the Optimist and the Realist.
Catherine, in terms of Vincent and his three bros: Orlando (the Cynic), Toby (the Optimist), Jonny (the Realist), and Vincent himself (the Conflicted, unsurprisingly).
Circle of Magic: Tris as Cynic, Sandry as Optimist, Briar as Realist, Daja as Apathetic.
The Hogwarts houses (and a generalization of their students) in the Harry Potter series:
The Optimist: Gryffindor
The Cynic: Slytherin
The Apathetic: Ravenclaw
The Realist: Hufflepuff
Last Scenario: Hilbert (the Idealist), Matilda (the Cynic), Thorve (the Realist), and Lorenza (the Conflicted). The other three party members are all Apathetic for some reason or another; Randolph is the "just along for the ride" variety, Ethan mostly keeps his thoughts to himself, and Zawu (and later Ethan as well) has a different set of goals and priorities.
Lonely Werewolf Girl: Kalix (the Cynic), Moonglow (the Realist), Vex (the Optimist) and Daniel (the Apathetic).
Beauty and Delicious (co-Optimists), Dominil (the Cynic), Thrix (the Realist) and Malveria (the Apathetic).
In The Three Musketeers, you have Athos as the Cynic, D'Artagnan as the Optimist, Aramis as the Realist, and Porthos as the Apathetic.
And in "De skandalösa", Magdalena (a Broken BirdStepford Snarker) is the Cynic, Gabriel (self-sacrificing, stubborn and impulsive) is the Optimist, Venus (another lovely but weak Extreme Doormat) is the Conflicted and Ossian (a Dork Knight, who will often take the middle ground) is the Realist.
From the Dragonlance novels: Flint is the Cynic, Sturm is the Optimist, Raistlin is the Realist and Tanis is the Conflicted.