A divide between Saudi Arabia’s ruling family and executives of the kingdom’s oil company over where to list the company’s shares is slowing the march toward a planned 2018 initial public offering, according to people familiar with the matter. Executives at Saudi Arabian Oil Co., known as Saudi Aramco, are pushing Saudi Arabia’s king and his son, Deputy Crown Prince Mohammed bin Salman, on the merits of listing the state-owned oil company on the London Stock Exchange. Executives believe that listing in the U.S. would…