They were a strange political or religious group that claimed that Humans were the rightful successors to the Orion people, either by nature or divine appointment, and that they had every right to invade and seize Orion territory. A total embarrassment to both the Federation and the Orion Colonies, the Earthly Brothers were given the harsh world of Gabok to settle and keep out of sight. They believed that they were performing a vital service, keeping the planet safe from the Klingons while terraforming it for the arrival of Human colonists. They numbered around 1 million Orions.
However, the Earthly Brothers were divided on obscure points of doctrine, and were unable to cooperate and form a functioning government, let alone organize a terraforming project. During the late 23rd century, only a handful of Gabok's inhabitants bothered with hydroponic agriculture or mining. As a result, they were entirely dependent upon the Federation for their very survival, and without food, clothing and shelter regularly delivered by Starfleet, the entire population was expected to perish within six months. (FASA RPG module: The Orions: Book of Common Knowledge)
- It's unclear if they survived those six months. It's also unclear if this is a cult or a political faction, a strange form of protest against the Federation, or a fan club, given the depiction of Orions in the source.