Cairo Trilogy by Naguib Mahfouz — The three novels (Palace Walk, Palace of Desire, Sugar Street) follow a Cairo merchant family through the first half of the twentieth century, the exact period when Heliopolis was being built and flourishing. Mahfouz is the master of Egyptian urban fiction and these books give the social texture of Cairo's bourgeoisie in a way nothing else quite matches.
Birds of Passage by Robert Solé — A novel following a Syro-Lebanese family in early twentieth-century Cairo, covering much the same period as the Mahfouz trilogy from a different angle. The Levantine Christian communities who settled in places like Heliopolis are at the heart of it.
Cairo: The City Victorious by Max Rodenbeck — The definitive modern history of Cairo in English: comprehensive, readable, and genuinely illuminating about how the city became what it is. The chapters on the colonial and early independence periods put Empain's project in context.
Rough Guide to Egypt or Lonely Planet Egypt — Either of the main Egypt travel guides will have practical coverage of Cairo and Heliopolis, useful for logistics and for placing the suburb within the wider city.