I'd have had the owl (singular) hover above the keep and wait for Lars and Timeon to finish the guard to transport them over to the gate house.
By the way: Timeon is an NPC so he should be able to use the trebuchet, shouldn't he?
Some (un)friendly fire on the gatehouse would be fun.
So, actions Round 3:
Simple action: Move to AT/58
Free action: Whisper (Auto success) hopefully reaching Aiden, Drin or Grumblejack in the dwarven vault.
Simple action: Move to BF 57
(I really need to pick up Fast Flyer or learn to use Haste)