I hope this isn't too late, but when you get to the fight with Private Mills, it would be a good idea to avoid the barrels as much as possible and try to get close to him as soon as possible, keeping your companions spread out so his barrages are less effective. As a Swashbuckler, you should have an easier time getting to him faster than he can set up traps.. He'll probably set up quite a few, but once you get to him, you should be able to take him out quickly with your Buckler damage. I suggest one or two long ranged companions for this fight.
For fighting the admiral, you must survive a few waves of enemies before actually getting to him. Make sure you pull your punches so that when he does show up, you can take him out. It might be a good idea to put some heals in the front of your Power slot for this battle, since this is all about endurance. You also might want a companion who has high health or one who can heal. Heal companions are pretty rare though, unless you have Wu Tang or Keisuke or the Bison Shaman or some others.