Thankfully, Viserys' Sense Motive skill is at +37 resting, and +47 with Air of Nobility, which he should be running right now. Even full Glibness shouldn't be able to steamroll that.
Preliminary plan.
[X] Inquire about the vial and what bargain he made for it.
-[X] "Although we have never made such a bargain ourselves, it might be something we would be interested in soon, as the years have begun to weigh heavy upon our shoulders and the resilience of youth is long gone."
[X] After speaking of the vial and Fey bargains, take your leave for now.
-[X] Attempt to arrange a meeting with Anglatine tomorrow during the midday break. If it cannot be done without disturbing her or her attendants unduly, we will seek her out as soon as the break begins.
-[X] Dany, with assistance from whichever Companions she feels necessary, especially Tyene, Lya, Malarys, and Richard, move to capture as many of Lucan's mages as possible while the Conclave is in service. They will be suitably disguised, both magically as well as by using mundane means.
--[X] They will place priority on capturing any of the more experienced mages who happen to venture out of their hideout.
--[X] If they believe it feasible, and Divination confirms it, they will move on the hideout itself. They will use Sleep-Smoke to quickly blanket the building's interior, along with mass incapacitation and capture spells, along with Forbiddance warding to prevent Teleportation if Dany believes it necessary.
--[X] Captured mages will be placed in Smoky Confinement bottles, if possible, and hidden in the Divination proofed room of the Shadow Tower until Viserys can place them in his cloak. Those which cannot yet be contained due to limited spell availability will be kept thoroughly sedated and under constant guard in the Divination proofed room.
--[X] They will be careful to watch out for disguised Outsiders, especially Gerold the Planetar. If Gerold is present, or similarly dangerous opponents, they will abort the mission.