Part of the premise for approval by state regulators was Twin River’s promise to spend what has become a full $100 million in upgrades on the outdated Bally’s property. But two years ago, that parent company sold Bally’s to Twin River Holdings of Rhode Island, as Caesars Entertainment was in the midst of purchasing Tropicana farther up the Boardwalk. For 15 years, the adjoining Caesars and Bally’s casinos on Atlantic City’s Boardwalk were “teammates,” as both were properties of the Caesars Entertainment parent company.