Tanic can fill you in.
The Mecrossan advisors and guards all brought concealable weapons into the meeting. The Imperial advisors (aside from you and Tanic) all did the same thing. Everyone jumped for cover; Tanic pushed Geful down, then snatched away a pair of blasters. He brought the fight to a swift end by blasting down Calthell's men and placing him at gunpoint.
Gallador did nothing to resist.