I've gotten to the tasting ceremony part of dampened spirits, but Commander Caius isn't there. Instead Mallus and some other guy who shouldn't be there are there, crouched down as if something's going to attack them. How do I fix this? If I can't, is there a way to completely restart the quest or move on to the next one?
Is Sabjorn inside Honningbrew Meadery? If yes, try speaking to him. If that still fails to advance the quest, try waiting for 3 in-game days and then go back to Honningbrew Meadery, and see if the NPCs have calmed down enough to allow advancing the quest.
If it still does not resolve the quest and you're playing on the PC, try using console commands. Once inside Honningbrew Meadery, open up the console by pressing ~ then type in:
prid 38258 (target Commander Caius) OR
prid 813BA (target Sinmir; only if you've taken Whiterun for the Stormcloaks)
moveto player (send targeted NPC to player)
If that still fails, try this console command instead:
setstage TG03 80 (makes the game assume that the event where Whiterun's Captain of the Guard drinks the poisoned mead is done)