Final answer:
In the 'Warriors' series by Erin Hunter, which is about the lives of wild cats, the sibling who discovers they are part of a prophecy is Jayfeather. He has the unique ability to walk in other cats' dreams and receives insights about the prophecy from the StarClan.
Step-by-step explanation:
The prophecy in question relates to the 'Warriors' series by Erin Hunter, which is a set of novels centered around the adventurous lives of wild cats. The sibling that discovers they are part of a prophecy in the 'Warriors' series is c) Jayfeather.
Jayfeather, alongside his siblings Lionblaze and Hollyleaf, explores the significance of the prophecy, which speaks of three cats with unique powers. While all three siblings have pivotal roles in the series, Jayfeather, with his supernatural abilities to walk in other cats' dreams, is the one who regularly receives insights from the StarClan about the prophecy and its meaning for their lives and the future of their Clan.
Jayfeather's discovery of their involvement in the prophecy sets the stage for significant events throughout the series and is a central theme that impacts the direction of the story.