According to Halacha, lighting ONE candle every night during Chanukkah is sufficient and a Jew does fulfill his Mitzvah. In Ashkenazi families each family member lights, at least, one candle. Sephardi Jews mostly follow a different custom and only the Baal HaBayit (the father) lights the Menorah.
The Vilna Gaon quoting the Rambam:
If you want to do it kosher Mehadrin min HaMehadrin, then you have to light eight candles. Meaning, add another candle every night throughout Chanukkah.
However, Jews who only light one candle (besides the Chamash) are still fulfilling their Mitzvah.