Balancing a 6 person party

[Donut_Druid]

So I'm running a Jade Regent campaign for a group of friends, and have no desire to kick any of them out of the game. They're about to come up on the final dungeon of the first module, and I worry how to make the dungeon challenging for them without killing them all off.
Party comp:
Catfolk Swashbuckler
Human Samurai (two handing Katana)
Tiefling Paladin (Greatsword focus, Hospitaller and Warrior of Holy Light archetypes)
Elf Wizard (Conjuration school)
Aasimaar Cleric (Shield and shortspear)
Skinwalker Ranger (Fanglord, Archery focus)
I would say that I'm a fairly experienced GM, but I've never run a party of this size, so any advice would be appreciated.

[Create Mr. Pitt]

Extra action economy, so more enemies and minions. The real issue here is that makes combat even longer. At least the wizard and cleric can add even more combatants. So the only way to challenge them is with more opponents, also favorable terrain for the enemies, and other things that balances out the very real action economy advantage of the party.

You'll want to get players to do their best to be efficient, prerolling attacks, having summon stat blocks ready to go, but even then prepare for combat to take up more time, so you'll either have less encounters, slower progress in the story, or some of the social interactions will suffer.