I'm also so curious about Eochaidh's perspective on all of this!
Is he guilty~?
Duped? Blackmailed? Deceived?
Was he fooled by Kaede to gather all of these people as 'bait' for the Erdrich summoning ritual?
If you're stuck, playing the blame game is always a fair option~ For instance, Eochaidh could have gotten the request to lead this expedition from someone even higher up on the guild, so the 'I was just following orders' card can always be played~
Brainstorming reasons why nobles might have been invited:
- It was worded as a joint "military exercise" -- practice to coordinate different factions/households. If it was an 'military exercise', it would potentially explain why @fyrre's character was invited (who is a student with minimal military experience).
- Nobles have special abilities that are related to their bloodline (like in Grancrest Senki). These special abilities were somehow specifically requested in order to complete the mission, but this would require each noble to be paired with a power that relates to the mission somehow.
- Feudalism. Perhaps every noble house is required to dedicate a certain amount of military service to the Queen every year, and this quest is a qualifying mission. The misleading quest description made it appear as though it was one of the 'safer' missions compared to the alternatives.
- Prestige. Some kind of special recognition was to be offered to the noble house(s) that cleared this mission. Example of desirable things include generic rewards (i.e. more land/money), but potentially promotions in noble rank (i.e. => marquis to duke). An example of something that might fit with the theme of the Sky Archipelago would be a temporary special butterfly (i.e. "A Golden Chrysalis") that when hatches would allow direct verbal communication with the Queen for a short period of time (~a few hours).
- Cold War. Cimon's Watch maybe has prominent strategic value. The faction that clears this mission would establish a sphere of influence over this area, so different aristocrats are indirectly competing with each other to control this airspace. This could explain why the Getandmark's brought six airships, because it would plainly broadcast to everyone that they intended to take control this airspace after the mission was cleared (in the South China Sea posturing sense).
It's a little hard to use the cultist angle to attract the nobles because Bochi has already established that that the nobles can't be allowed to know about the true purpose of the mission. If they were presented as too much of a threat, a lot of the invited parties would undeniably ask a lot of questions, and the mission absolutely wouldn't be labeled as a "scouting mission".
Anyways, those were some quick random ideas!