From the ordinance
Family. A person living alone, or any of the following groups living together as a single housekeeping unit: (1) Any number of persons related by blood, marriage, adoption, guardianship, or duly-authorized custodial relationship; (2) Four (4) unrelated people; (3) Two (2) unrelated people and any children related to either of them; (4) Residents of an assisted living facility or group home as allowed by Code of Virginia, § 15.2-2291.