“The deed is done. There's no going back. We are your family now.”
The Sovereign Family are one of the largest criminal organisations in the Elysian Empire, with fingers in a huge variety of pies, from theft and protection to smuggling and drug dealing. They take the loyalty of their members very seriously, and are known to have an elaborate set of rituals, customs and oaths. The highest-ranking members (known as “Ancestors”) are mostly descendants of the founders of the organisation, as was the last known leader, Allison Gold.
Sources vary on just how influential they really are, with official publications claiming they're much less of a threat than many rumours (possibly started by the Family themselves) would indicate. In regions where they're strongest however, their influence is undeniable, and the authorities are too busy with the war effort to properly stamp them out.
Rumour has it that they even have their own interstellar ships for smuggling, as well as for occasional acts of particularly nasty revenge. Although their reputation is mostly for ruthlessness, they are also regarded as honourable, by criminal standards at least, and are thus often employed to arbitrate and enforce illegal contracts, helping to keep the black markets &c. running as smoothly as can be expected.
They use familial relation words for their hierarchy, e.g. someone's direct superior is called their “Parent”.
The Family are one of the most secretive of the large gangs in the prison, although even their standards of loyalty don't always hold up under torture. Nonetheless, they at least try to keep an air of mystique about their activities, and are sufficiently organised that the guards usually find it easier not to pry too much.
They evidently have less control over the prison than they would like, but their experience at exploiting corruption hasn't been wasted. They have managed to some extent to continue within the prison their main business of protection, but the prison's security measures and the prevalence of violence in the prison in general limit the effectiveness of this approach.
Full membership is mostly limited to those who were initiated before being sent to prison. Any oaths made in such a desperate situation as this can't be properly trusted. A few have joined as associate members, but there's not much incentive to do so with little hope of promotion.