I have this headcanon that subjuggulators will enslave other indigo bloods that aren't part of the cult. slaves are branded in some manner, either with a hole drilled through the horn or forced to wear their master's symbol or paint pattern.
This is possible. Enough people headcanon there being slightly more and less vicious sects even within the cult (they're ALL vicious, just some less so). So some might do this and others might not.
I think there are basic beliefs they all hold, or else their carnival get called heretical and hunted to extinction, but other than that, each carnival has its own ways of doing things. Alypho's seems to be pretty chill, and he hasn't tried to enslave or even chucklevoodoo Akhena into the cult, which i'm sure some subjugs would try to do.
Then again I also sort of headcanon that above about cerulean, you're not going to become a slave except MAYBE to seadwellers. (a tyrian could probably have whoever they want as a slave tho, they're basically gods/goddesses in troll form.) subjugs might not like a disbeliever, might try to intimidate, chucklevoodoo, brainwash or just plain physically force a non-believer to join the carnival. they might kill a non-believer for their heretical ways. but they won't make them a slave.
indigos, especially indigos who believe in the Messiahs, believe they are the top landwellers, and a lot of them will only grudgingly say that seadwellers are "above" them in the social structure. And the ones who DO believe they are the Messiahs' chosen ones? a lot of them think that the fish would be better off gone and dead than trying to lord themselves over landdwellers. this comes from another headcanon i've seen that landwellers and seadwellers (maybe even low-, middle-, and highbloods on land) were different cultures and the seadwellers took over at some point. so they wouldn't be too keen on giving other indigos to the seadwellers, especially as slaves.
but tl;dr i think most would try to convert the other indigos, sometimes by force. the new converts would be at the bottom of the totem pole, but they wouldn't be slaves, at least technically












