The theives were not in any way part of the main story, unless they were the theives that hid under the Light World Theives Town area. One thief gives Link 300 rupees for Link to not tell anyone about him, one tells him about the cave in Lake Hylia with the Golden Bee, fairies, and the Ice rod, one tells Link about the member of the gang near the entrance to the desert that knows how to unlock any lock. Basically, they give clues on how to get the 4th bottle and the Ice rod, and give Link some spare cash. One thief runs a gambling game in the northeast part of the Lost Woods.