-- Tsukino family (Usagi) --
Tsukino Ikuko - Usagi's mother. She is a tall, pretty woman with flowing purple hair; she seems like a pretty nice lady. She does not seem to have a job, but sits at home cooking, cleaning, and reading the newspaper. She is tolerant of her daughter's tendency to bring home strange cats with bald spots; however, she has very little patience with Usagi's bad test grades. Like any good mother, she is concerned for her daughter's welfare, and becomes worried when Usagi is downcast or depressed. The Tsukino family lives in an unremarkable two-story house in the Juuban district of Tokyo. She is named after Naoko Takeuchi's real life mother, Takeuchi Ikuko.
-- Mizuno family (Ami) --
Tsukino Kenji - Usagi's father. He's a rather ordinary looking man with short black hair and glasses. He seems like a decent father; he tries to make Usagi happy, and seems rather protective of his daughter when it comes to guys. (Which is a completely normal reaction for any good father.) He also laughed at Usagi when she proclaimed herself to be Sailormoon. He is a magazine editor at an office; he was able to go to Princess D's masked ball as a reporter. He is named after Naoko Takeuchi's real life father, Takeuchi Kenji.
Tsukino Shingo - Usagi's little brother. We don't see much of this boy, really. He's a typical little brother - he teases Usagi mercilessly, taunts her about her grades and her homework, and generally acts a little bratty. He has green eyes and blond hair. Apparently, he loves Nintendo and boy's manga. (And no, I have no idea why neither of the Tsukino children look anything like their parents - lucky genes, I guess.) He is named after Naoko Takeuchi's real life brother, Takeuchi Shingo.
Ami's mother is introduced in Act 2, but we don't see her face until Act 35. She is tall and pretty with short-cropped black hair. She is also a successful doctor; it is alluded to several times that the Mizuno family is very rich. (After all, Ami could afford to go to expensive cram schools like the Crystal Seminar.) They live in a luxurious condominium with marble flooring; when Mina chipped Ami's diamond, Ami dismissed her apologies with a casual "My mom has so many of these, it's sick." It's obvious where Ami got her work ethic; her mother's a single parent, and she must work very hard to support her daughter so well.
Ami's father left when Ami was young. He's a famous Japanese master painter who loves relaxing in nature; he travelled all over the world to find things to sketch. In his infrequent time at home, he taught his young daughter to swim and play chess; his wife got very little attention from him. One day he capriciously decided to stay at his forest study; abandoning his daughter and his wife, he never returned home. He still sends Ami postcards on her birthday.
-- Hino family (Rei) --
Hino-san, or Rei no ojii-chan - Rei's grandfather. He basically raised Rei alone when her mother died and she refused to stay with her father. Rei is very protective of her grandfather; he's the only member of her family that she feels that she can turn to for comfort and love. For his part, he's happy when he sees Rei happy. He's a fragile old man, and she tends to fuss over his health. (By the way, he is nothing like the old hentai he is in the anime. He does at one point call the other girls pretty and invite them to become shrine maidens, but this was more to get a rise out of Rei than anything else.) He owns the Hikawa Jinja Shinto shrine at Sendai Hill, where he and Rei live.
Rei's father is a big-time politician for the Democratic Liberal Party (Naoko-san's analogue to the real-life Liberal Democratic Party). He almost completely ignores his daughter's existence. He treats her more as a business associate than a family member; he told his assistant Kaidou to buy her birthday presents and take her out to dinner. Her father's neglect shattered Rei's belief that she could have faith in people. We never really see his face; he seems to be blond, bespectacled, and has a moustache, like Rei's grandfather.
Rei's mother died when Rei was young - but not too old to remember, and understand what was going on. Rei understood that her mother was lonely, because there was no room in Rei's father's mind for anything but politics. He neglected his wife and daughter equally, while they pined after his love. Rei's mother eventually became weak, and died with only her daughter for company. It's obvious that Rei resembles her mother greatly; they are both lovely and slender, with long black hair.
Kaidou is not exactly a member of Rei's family, but he had a hand in her upbringing. He is Rei's father's top assistant, and Rei's father basically assigned him to take care of Rei. It was Kaidou who picked out Rei's birthday presents, and complimented her on her growing beauty. He said that he shared Rei's feelings - that he didn't want to marry and have children, because he didn't want them to be unhappy like Rei; this prompted Rei to say that they were kindred spirits; she fell in love with him. Soon after that conversation, however, she saw him with another woman; Rei discovered that Kaidou was actually getting engaged to the daughter of a wealthy businessman. (A very politically shrewd move.) This experience left Rei with the determination never to look back on the pain of the past, and never to marry.