Having some trouble.

[tribble]

I'm pushing for a religious victory with my cthulhu-worshipping Lanun, but I've run into some problems.

-Beeri Brawl is my vassal. I have instituted the OO religion in every one of his civs, but he wants me to pay him to switch state religion from Runes, even though OO is in more of his cities. Furthermore, if I do pay him to switch, he switches back immediately. What's up with this?
-I can't even ASK Thessa to convert to OO, although it's in almost all of her cities. Like, it doesn't appear as a red option in diplomacy, it just isn't on the proposal menu at all. I'm having the same problem with the leader of the Khazad, whose name eludes me at the moment.
-Because more world influence is never not a good thing, I sent my army to capture a barbarian city. When I crushed the defenders my unit automatically razed the city. I've captured cities with elementals before, so what's going on here?

 

[Emptiness]

-Beeri Brawl is my vassal. I have instituted the OO religion in every one of his civs, but he wants me to pay him to switch state religion from Runes, even though OO is in more of his cities. Furthermore, if I do pay him to switch, he switches back immediately. What's up with this?

Religious victory does not require that anyone follow the winning religion. Even the winner doesn't need to follow it.

If you are trying to get your vassal to convert so that you can inquisition the other religions from its cities, then you don't actually need them to remain in OO. Make one priest for each of the Luchuirp cities, promote them all with Inquisition, and start them casting on the same turn. Pay the Luchuirp to convert to OO the turn before the Inquisition takes place, and then on the next turn all the other religions will be removed from their cities. (As an added benefit, this will probably also make them stay in OO.)

-I can't even ASK Thessa to convert to OO, although it's in almost all of her cities. Like, it doesn't appear as a red option in diplomacy, it just isn't on the proposal menu at all. I'm having the same problem with the leader of the Khazad, whose name eludes me at the moment.

The option doesn't appear if the civ is not eligible for conversion. This can happen if a civ has recently converted to another religion, for example. There may also be other reasons why the option to ask for conversion doesn't appear.

If you don't see the option you can either check back each turn until it reappears (if it ever does - sometimes a civ will get into a cycle of flip-flopping between two religions), or you can convert their cities by force.

-Because more world influence is never not a good thing, I sent my army to capture a barbarian city. When I crushed the defenders my unit automatically razed the city. I've captured cities with elementals before, so what's going on here?

Size 1 cities with no culture are always razed.