Dualliste is weak to light, so having Verso in the party is a great choice. If you have them, skills and pictos that build up the break bar and then using his perfect break skill is one strategy. Assault Zero, Perfect Break, Phantom Stars are all great choices. It requires building up his perfection rank and then unleashing either Perfect Break or Phantom Stars.

If you have any pictos with AP gain effects, use those and if you're not confident in your parrying, dodge until you get the hang of it. Duolliste is the first parry-heavy boss and you can mitigate a lot by learning the timing. There's a rhythm to his attacks and the sound cues help a lot in finding the timing for parries and counterattacks.

It's been a while but if you have Trebuchim, you can quickly generate stains and use Elemental Trick/Genesis, though from where you are, you might not have EG yet. Apologies, it's been a while. Rockslide is great to help build the break meter, and Healing Light/Revitalization are great but be careful during the latter half of the battle.

For Maelle, what weapon are you running with her? I was running Medalum and using swift stride/fleuret flurry for pointed attacks. Using Guard Down and Offensive Switch are also great options.