The Kunou Family
Kunou Tatewaki Kunou-senpai, Blue Thunder of Furinkan High
(Commonly referred to as simply Kunou) He had been the big boss at Furinkan High School until Ranma's appearance; he still is the big bully. He was the one who proposed the challenge that the one guy who could defeat Akane in battle could date her, leading to Akane's fights every morning at school. This finally ended when Ranma came and beat Kunou silly.... Kunou himself is very much in love with Akane and Osage no Onna, his Pigtailed Girl. That's right, he doesn't know that Ranma-kun and Ranma-chan are the same person, only different forms (despite the numerous times that Ranma has shapeshifted right in front of Kunou). Kunou is constantly wearing his kendo outfit (minus the armor) and carries his bokken (wooden sword) with him everywhere. He is very, very skilled with the bokken (he can cleave rock with that thing), but still is routinely thrashed by Ranma whenever they fight. Kunou is the older sibling.
Kunou Kodachi The Black Rose
Kodachi attends a rival high school of all the other teenagers (at least, those who go to Furinkan High School). She seems to be constantly wearing her purple leotard and carrying her ribbon for martial rhythmic gymnastics. She also specializes in fighting fair--well, fighting in a way that's fair to herself. Most often, in martial arts/gymnastics competitions, her opponents don't ever show up, owing to a few exploits a little before the competition. She loves plants, and commonly calls herself the Black Rose (one of her pre-comp specialties is a bouquet of black roses that puff out paralyzation gas). She has fallen in love with Ranma-kun, and is always arguing with her brother about Ranma. She, like her brother, is so clueless as to not realize that -kun and -chan are the same person, and hates Ranma-chan. Oh, yeah, she's also flipping INSANE, with an evil laugh to back that up. She is the younger of the Kunou siblings. I kinda feel sorry for her--always had empathy for humorously crazy people %)--and right now, I'm writing a fic about a guy who falls in love with her. To be posted someday....
Principal Kunou Kunou-kouchou
Many years ago, Mr. Kunou disappeared. He recently returned wearing rather distatsteful Hawaiian clothing, including this bonsai palm tree that somehow manages to stay perched on top of his head. He is now the principal of Furinkan High, and is constantly at odds with Ranma (as well as the rest of the student population). He once attempted to establish a school rule that all the females wear their hair above their shoulders and all the males have their heads shaved, and Ranma was to be the example. As can be seen by the existance of Ranma's ponytail, he failed. He still carries his shears around in the high school and tries to give impromptu haircuts in the halls.
Sasuke isn't really a member of the family, but he's around the Kunous often enough.... Sasuke is a ninja hired as a servant/handyman/spy for the Kunou mansion, and handles all the security (especially all the traps). He is overworked and underpaid, and one can't help but feel a little sorry for the guy. (Note--he only appears in the anime.)