Well, Slavin and Valeria were on the outside of that whole thing. They were simply hired to do a job (a job which interestingly enough had NOTHING at all to do with the Fourth Ring's plans at all ... something for which even Ivor was just hired help). Leon Cavallo was another one who was just a hireling, an ally that helped lend the circus a new level of authenticity. Eventually, he became a pawn as well, infected by Ivor as a smokescreen to keep people from asking the question about why the circus folk seemed immune to all that was going on.
Within the Fourth Ring, there was a mixture of other types as well. There were those who were a part of Ivor's circus, which was messed up enough as it is, a group tied to Ivor's past and his twisted interpretation of a family. Characters like McCadish fit into that mold. And there were others who were agents of the larger Fourth Ring, an evil cult of which Ivor and his circus only made up one part. Kevin and Tyx are good examples of that. And then there are those who were a bit of both ... members of Ivor's circus family and privy to their own goals, but also dedicated followers of the broader Fourth Ring and dedicated to their goals as well. The Popescus and perhaps Avie Cline fit into that arena.
There is another aspect of the Fourth Ring that we tried to follow in terms of differentiation. The plague was a creation of Ivor himself and it operated according to his design. Gomorra's design was not the first incarnation of it, nor would it have been the last. As its source, however, Ivor also contained a cure for it, which would halt its progression and relieve all symptoms. However, it would not "undo" the damage already done. So most of the more "deformed" members of T4R actually carry Ivor's plague within them (which earns them the Abomination keyword as well). But the degree to which their appearance and physiology may have changed is determined by the version of the disease that Ivor infected them with originally, as well as how far he allowed it to progress before "curing" it. So Funtime Freddy and Junior fall into those categories. This also explains one of the biggest questions that the playtesters and the design team had at the time, which was why Karl Odett (whose playtest name was "The Sum of All Fears" BTW) was an Abomination, given his name and artwork. Even though he looks more or less normal, he actually carries Ivor's plague as well and even exerts some level of control and influence over it in others. He truly IS an abomination, and one that is more dangerous the more he is surrounded by them. But the nature of the disease and how Ivor manipulated and "cured" it actually allowed him to remain fairly normal looking, which made him the perfect choice to look after the Sanatorium on Ivor's behalf.
Given the limited story space within the game, these are details that we could never explain fully, but ideas that we developed and operated by as much as possible to create a cohesive story, even in details that may have never been fully understood by the reader at the time.