[X] Let sappers use some of the Darkenbeasts companies Explosive Packs to blow down the outer walls, then call for surrender again, making it clear that the next step if they refuse is to throw a mix of firebombs and explosives from the Darkenbeasts, which will see the keep reduced to burning rubble.
-[X] The Darkenbeasts will circle the keep to keep the garrison from interfering with the sappers.
[X] Challenge the Lord to a duel under his own terms. If he should be so cowardly to refuse to accept, challenge the person with nominal command of the garrison under the same terms. If he should not, point out that the next step is to blow up the gate with a lightning bolt, and so help us if we find a dead household...