Sibling (rank)

You may be looking for the actual family relationship.

The rank of Sibling (sometimes gendered as Brother or Sister) was occasionally granted to members of Faction Paradox, signifying a member who had been in the Faction long enough to no longer be a Little Sibling, but had not formally been initiated to the rank of Cousin.

History

Brother Signet was active in the Eleven-Day Empire. (AUDIO: The Confession of Brother Signet, Lucifer)

The Family of the Shadow Spire, being the splinter group of the Faction which had coalesced out of those who had taken refuge in the Shadow Spire after the destruction of the Eleven-Day Empire, included "a couple older Siblings", including Brother Gustav and Brother Intrepid. (PROSE: Going Once, Going Twice)

Sibling Same and Sibling Different were speculated by the Thirteenth Doctor to have originally been members of the Faction who had survived through the Last Great Time War, although none of them could be sure of this, as their past was time locked out of reach. At any rate, she advised them to seek out other potential survivors of the Faction. (PROSE: The Paradox Moon)