1. A twin city is one that is commonly called that, such as St. Paul, Minnesota and Minneapolis, Minnesota. It should have multiple WP:RELY citations indicating this.
2. A divided city is an existing city that has been divided for some reason between two distinct governing bodies, such as Berlin, Germany was from 1945 to 1991.
3. A city that has "grown together", most notable Buda and Pest into Budapest, Hungary falls into neither category. Many municipalities have grown together. This is not a special category.