Baron Robert Fairchild, a pure-blood, made an inebriated mistake while wandering through the village that he ruled one night. That mistake wound up with the pregnant Adelaide, a Muggle. To avoid both her shame of unwed motherhood, and his shame due to scandal, the two married, quickly and quietly. Robert never told his new wife about his magical abilities, and nine months later, Geoffrey Fairchild was the result.
Two years later, however, after the couple had fallen something in love, Adelaide wound up pregnant again. This time, the child was a girl who they called Maeva. With Geoff as the heir already, Maeva was tossed to the sidelines, and Geoff was given all the attention and favoritism, despite not being a well-planned child, either.
When Geoff was five, and he accidentally set his father's curtains on fire, Robert could no longer hide his secret, and came clean to Adelaide. Another six years later, Geoff received his letter to Hogwarts, and off he went. He is now a seventh year.
Geoffrey grew up in the limelight his whole life, and he wore it with pride. He adopted his family's feelings for Maeva... also casting her to the side. It's not his fault that he was born a boy, and she wasn't, and so he doesn't really treat her very nicely. If he must interact with her... it's cordial at best, snide at the worst. Additionally, worried that he'll be saddled with his unwed sister when he inherits his father's title, he is actively seeking some kind of betrothal for her.
Robert Fairchild: Geoff's father. Geoff and his father were always close, due to the fact that Geoff will one day inherit Robert's title and money. Geoff grew up watching the way that Robert treated Adelaide and Maeva very closely, and the way Robert treats them, so does Geoff.
Adelaide Fairchild: Geoff's mother. When Geoff's first signs of magic appeared, Adelaide was very frightened of both her husband, and her son, and Geoff became confused and a little hurt. Since then, since Robert treats Adelaide with some respect, so does Geoff, but they aren't close.
Maeva Fairchild: Geoff's younger sister. Since Robert treated Maeva as nothing but an extra burden, Geoff adopted some of those same habits. If he must speak to her, it tends to be in either a long-suffering tone of voice, or a snide one. He's told her (once) that her one gift to him is her pretty face-- she'll be easy to marry off. They aren't close.