Sibling Rivalries has a lot of interesting characters, most of them having also appeared in Cletus Comics, and many also reappear in the prequel Sibling Rivalries: Salvador Real's Adventures and Sibling Rivalries: Vancouver Stories.
- Characters (Characters from Cletus Comics not included)
- Patrick "Packie" McReary: The protagonist of the story, and the characters the readers see the story from. He is the so-called "normal" person of the McReary Family, an Irish-American family from Canada. He has no problems with making friends, and makes a lot in the storyline.
- Francis McReary, Gerald "Gerry" McReary, Derrick McReary, Kate McReary, and Maureen McReary: The rest of Packie's family, the first four being his siblings, and the last being his mother. Packie relates to Francis very well, but often sees differences in Gerry, Derrick, and Kate. He still loves his family very much.
- Angel Chacon, Michelle Stone, Salvador Real, Jose Gonzales, Tony Gonzales, Salvador Martinez, Pablo Torres, and David Saldivar: The people Packie likes (besides Francis and his siblings), and relates to them very well. Angel and Salvador Real seem to not like him at first (the latter being sarcastic, and the first hating Packie for not being a good football substitute), and Pablo not trusting him near his sister, the other few like Packie from the start, and Packie talks to them the most.
- Joel Gonzales, James Johnson, and Giovanni Ancelotti: The people Packie doesn't like because of their disloyalty (the latter being unseen), and eventually become Packie's enemies.