Complex sentence: The story takes place before the existence of Batman's sidekick Robin, and Batgirl, although Robin appears as a playable character outside of the main story, and Barbara Gordon appears in the main story.
Split into simpler sentences: The story takes place before the existence of Batman's sidekicks Robin and Batgirl. However, Robin makes an appearance as a playable character outside of the main story, and Barbara Gordon appears in the main story.