Whatever the case is, the stones give access to Cleopatra's burial chamber and also to her treasury, which the heroes claim possession of and later give to charity. The original Japanese ending, on the other hand, says that "when all three stones become one, their power will change the world". To add to the confusion, the English ending text says that "when the third stone is found, its power will change the world", implying that they never found the third stone and probably that's why they were attacked inside the pyramid in the first place.
The third stone's whereabouts is somewhat left to ambiguity, as the game's limited storytelling (both textually and graphically) isn't clear if it was in Hiruko's possession all along (as it happens with the fourth stone in the NES/Famicom version), and/or if there was a fourth stone that altogether allowed safe passage into Cleopatra's burial chamber, where four stones can in fact be seen encrusted on golden tablets on the chamber's walls (although these could merely be design aesthetics and actually be unrelated to the Rosetta Stones). The second stone is found in Japan, in possession of a skillful ninja master known as Yagyu Ranzou. In the arcade version, the first stone is found in China, held by a powerful Kung Fu master known as Li Cheng-Long.
1.2 Double Dragon III: The Sacred Stones.