The plan was simple. The scenario they intended to create was a hostage situation where Ardyn would pretend to be the bad guy and threaten the villagers into letting his friends go in exchange for Beatrice's life. Solana would be the one to warn the villagers about the sudden ransom situation that she had unfortunately "witnessed".
If the villagers tried to break down the door by force, Ardyn would have to convince them not to do so, otherwise Beatrice's life would be in danger. It would work even if he was just in the room next to the one Beatrice was in, because the walls were supposedly not soundproof, and noise would easily filter through the walls as long as it was loud enough, like someone screaming, and others would very likely mistake it for them still being in the same room.
