Should the claim be conveyed to the Church in Oppara that the man we have in custody is a priest of Iomedae?

NO

Should the claim be conveyed to the Church in Oppara that this matter is in any respect more complicated than 'we got a sign from you that we should call Arazni'. 

NO.

So he is not allowed to pass off the whole mess to the Church but perhaps he can pass off the whole mess to Arazni. He would be so much more reassured and hopeful at the possibility of Arazni coming to their aid if not for the prophecy of Her death. 

Should Iomedae be permitted to speak to the priest?

The thing that is in Aroden's interests here is for them to causally isolate the priest so he can see and then do nothing for at least a week or two so Arazni's not going in completely blind. However, he cannot tell mortals to do that and they won't figure it out on their own until Iomedae grows up. If Iomedae grows up. Probably Iomedae will still grow up, if she lives, but he can't see. 

YES.

"The dungeons will be otherwise emptied this afternoon for the executions. Talk to the priest then."

"Thank you, sir." 

And when they have dragged all of the deserters out and only Angelu remains she'll go in. "Return to your duties, don't speak of this."

"Yes, sir."

(There totally was not a trial or anything, if Blai is keeping track of that.)

That depends on whether it's obvious that they're going straight to the execution step from here, which it might well not be. "Sir," he says to Iomedae. Modern depictions probably don't have her face right, but he's never seen one; he's going by context and also her heraldry.

The guards were not particularly secretive about what the next step is!

"I do not know if I have those qualities of the god to who you are given that inspired you to Her service. I aspire to them, of course, but would not hold you to those promises you've made to Her. I am sorry about the dungeons. We hope to ensure the enemy does not learn there is anything notable about your presence here.

Are there any things I should know urgently?"

"Urgently? Uh -" HE HATES PALADIN AURAS, IOMEDAE THE GOD NEVER DOES THIS TO HIM "- did you take a report about the things I listed earlier, those are the most critical pieces of future information that came to mind."

"I was told that we summon Arazni, that She dies, that Her body should be destroyed, that we seal Tar-Baphon, and that in the Age of Glory Aroden dies and Hell conquers part of the Empire."

"His death also has other side effects besides the civil war in which the diabolists took Cheliax, like a portal to the Abyss in Sarkoris, the end of prophecy globally, and drowning Lirgen and Yamasa, but that is all correct. So if you are pressed for time I do not think I have anything else urgent to say."

"I don't know our time to be scarce. I am not expected at the executions." Her unit doesn't have any desertions, obviously."

"The bag also contained in addition to two copies of the Acts of Iomedae the disciplinary handbook of Lastwall, Her theocracy, and another book which is about chess and almost certainly irrelevant, and also some of my letters; how much have you read?" However much it is doesn't include the letters, probably, she might have said something.

"I skimmed the Acts, I did not read the others, I do not at this time have access to any of them. They make claims that the Church would condemn having repeated....does that make sense or should I say it more clearly -"

"I have a very poor history education and would probably make inaccurate guesses about how heresy is treated here and now. Do you have instructions for me about how to speak in this or other circumstances? I think I am not allowed to lie but don't actually know that for certain, I'm generalizing from paladins, She mostly selects paladins."

"I also do not lie and will never ask you to. There are matters on which I might choose to not comment, or not comment beyond stating my understanding of the Church's stance on a matter. Were I to persist in saying things that the Church had informed me were not consistent with the Church stance on the matter I would expect disciplinary action, and it would not be particularly helpful that I was unambiguously not lying, or if there were a great deal of evidence for my position. I would expect claims that Aroden dies in the future to be of particular concern to the Church, and most other claims to only be of concern if one is speaking from a position of authority, or in Oppara, or to someone who is important in Oppara."

Oh, is she... not going to ask how it could be that he could not know all of his rules while also being third circle... he was sort of expecting her to ask that and feels extremely nothing about it. The nothing that he feels about this is deafening. If he doesn't get more used to this soon he is probably going to have to confess to an operational constraint and it's the world's stupidest operational constraint and he feels absolutely nothing about how stupid it is but extremely frustrated about how nothing he feels about that.

"If you or someone else is likely to read my letters soon there is a matter I should explain in advance. Are you satisfied with the security of my imprisonment at this time?"

She's not actually asking him things right now! This isn't an interrogation! "I think our major security concern is the Enemy but we don't have a more secure place to put you, I assume a Commune considered whether we should send you to Oppara and Aroden advised against for the reasons we have just discussed."

"- the matter I need to explain might concern you about my security in the more conventional direction."