What are your men’s unit stats, and did you mentor one of your Lt’s?
And do you mean when Caz stops your first action before defending the docks? If you’re referring to that, Caz will always foil the first action you order that involves going out to the city unless the dragoons help the Cuirassiers against 3rd in front of the Northern Keep when they show up.
Might be worth noting going to Takaran embassy for weapons (if Palliser’s blockade was broken) is exempt from this rule, even if it also involves going out to the city. As is gathering stuff for barricades, but that’s more obvious since you don’t leave the docks area.
You probably mean at the Northern Keep. Keep your men in reserve all the way once Caz appears, until the option to do a fighting retreat appears. You will automatically succeed regardless of stats.
Nearly all other options require your dragoons to be very well trained. You will need at least 40 in discipline and morale for both 1st and 2nd squadron and more than 75 str each, unless you have a fully mentored Sandoral or Blaylock which would alleviate those requirements a little.
I still feel that battle is way too hard to be fair - the required stats are way too high - but that is one way you can win.