I like the idea that the Cult of Shallya contains a ton of lamians. It's just that they're actually loyal. If they are part of the conspiracy, then they put serving it below serving Shallya. A temple needs funding, y'know.
They, the totally loyal conspiracy lamians, are just there to keep an eye on those maverick lamians, which is a very hard task since they certainly don't have weekly tea parties, and so it requires all their attention. And also funding, because there's a lot of decentralized temples that need an eye, and somehow more just keep popping up. No idea where they get the money, but we, extremly loyal members of the conspiracy, certainly need to keep an eye on it.
So that's my Vampire Mathilde and Heidi shipping AU. It's obviously total crack. No, since the biggest problem of vampires is feeding, the actual religious vampire conspiracy sect is part of the church of Esmeralda. The Moot, after all, is directly next to Sylvania.