In the original 1001 Nights' "Aladdin" (Windermere Series translation as indicated in an answer here), the following passage indicates there was more than one genie in the lamp (emphasis mine):
Aladdin's mother took the lamp and said to her son, "Here it is, but it is very dirty. If it were a little cleaner I believe it would bring something more." She took some fine sand and water to clean it. But she had no sooner begun to rub it, than in an instant a hideous genie of gigantic size appeared before her, and said to her in a voice of thunder, "What wouldst thou have? I am ready to obey thee as thy slave, and the slave of all those who have that lamp in their hands; I, and the other slaves of the lamp."
There does exist a genie bound to a ring in some adaptations, and according to the Arabian Nights wikia, an 1826 opera names 3 female residents of the lamp:
In the fairy opera of Aladdin by G. Soane (1826), there are actually three female genies of the lamp named Astra, Mellora and Corella.
Is there any indication as to the actual number of genies in the lamp?