Don't.
The antagonists want the PCs alive--that's already been established. So let the players take a few runs at the guards; undoubtedly one time they will come up with something clever or amazing, which'll work. Let your players solve the problem for you.
(In addition, your players aren't actually that diminished by their lack of equipment. I cover that in "part two" of this answer.)
Why do we balance encounters?
Generally, we don't want to TPK unless the players ignore lots of warning signs and do actively stupid things. And we don't like a deus ex machina where the wires and ropes and assistants turning the crank are all visible. So we worry about balancing the encounter, making sure it's a challenge while ensuring player victory, and the game becomes about how few of their resources they can burn during any given encounter.
None of this applies here. Your players have a limited set of resources, but that's not going to stop them from making a big stink: the druid can still wildshape, the barbarian and paladin can still do tremendous--compared to an NPC's life--damage bare-handed (Divine Smiting left and right, literally!), but your fighter or rogue might be relegated to Helping the wizard make creative use of the one spell they have without material components.
Remember, the party need not kill too many NPCs before they'll run for help, allowing you to transition to a chase/escape scene. I mean, how many redshirts are really willing to die for their cause? Usually they don't have a choice, because we back them into a corner or gun them down from behind for XP. But this time the NPCs have plenty of 'outs,' and the players should be happy to let them use one.
And maybe the party fails, only to try again another day. It may feel a little like Groundhog Day. But that's no insult--that's an awesome movie.
Your party:
You've added a bit of detail, so I will too =)
The tl;dr is your party is still well-equipped, even when unequipped, to handle themselves. They're down some ranged attacks, maybe. They're down a little damage output from the martials. They're down some AC, again mostly on the martial side, but you've got plenty of healing.
There's plenty of room for creative combat solutions with what's left:
Your cleric has access to Blindness/Deafness,
Burning Hands,
Calm Emotions,
Charm Person,
Chill Touch,
Command,
Cure Wounds,
Detect Evil and Good,
Detect Magic,
Disguise Self,
Divine Favor,
Druidcraft,
Faerie Fire,
Find Traps,
Fog Cloud,
Guidance,
Guiding Bolt,
Healing Word,
Inflict Wounds,
Lesser Restoration,
Magic Weapon,
Mirror Image,
Poison Spray,
Prayer of Healing,
Produce Flame,
Protection from Poison,
Purify Food and Drink,
Ray of Enfeeblement,
Ray of Sickness,
Sacred Flame,
Scorching Ray,
Silence,
Spare the Dying,
Speak with Animals,
Spiritual Weapon,
Thaumaturgy,
Thunderwave,
Zone of Truth, all without material components. (Some might depend on domain.)
Your druid has access to Beast Sense,
Blur,
Charm Person,
Cure Wounds,
Detect Magic,
Druidcraft,
Entangle,
Faerie Fire,
Find Traps,
Fog Cloud,
Guidance,
Healing Word,
Lesser Restoration,
Mirror Image,
Misty Step,
Poison Spray,
Produce Flame,
Protection from Poison,
Purify Food and Drink,
Silence,
Speak with Animals,
Thunderwave, all without material components. (Some may depend on circle/land.)
And they can turn into a bear! Or a mouse. Either might be very useful.
Your fighter can punch a dude and still do 1+STR damage, and can grab any ol' thing lying around to do an expected 2.5+STR damage. Assuming +3 STR that's still ~2/3 the damage you might have been doing be-weaponed. (That assumes same likelihood to hit--I like to give my fighters proficiency with almost any improvised weapon: the defining characteristic of the class is training with all types of weapons and combat, so I give them the most latitude with improvised weapons, too.)
Or they can Help their allies, or grapple, or shove... maybe this is the fight where the fighter isn't the character to take the prize for damage dealt. That's cool, too.
Your paladin has access to Branding Smite,
Command,
Compelled Duel,
Crown of Madness,
Cure Wounds,
Detect Evil and Good,
Detect Magic,
Divine Favor,
Ensnaring Strike,
Find Steed,
Hellish Rebuke,
Heroism,
Hunter's Mark,
Inflict Wounds,
Lesser Restoration,
Magic Weapon,
Misty Step,
Protection from Poison,
Purify Food and Drink,
Searing Smite,
Speak with Animals,
Thunderous Smite,
Wrathful Smite,
Zone of Truth, all without material components. (Some may depend on Oath.) But you're probably better off spending those spell slots Divine Smiting with your fists.
Your ranger has access to Beast Sense,
Cure Wounds,
Detect Magic,
Ensnaring Strike,
Find Traps,
Fog Cloud,
Hail of Thorns,
Hunter's Mark,
Lesser Restoration,
Protection from Poison,
Silence,
Speak with Animals, all without material components. Actually, those don't look terribly useful. But you're a ranger, so you should be used to that.
Your sorcerer has access to Acid Splash,
Alter Self,
Blade Ward,
Blindness/Deafness,
Blur,
Burning Hands,
Charm Person,
Chill Touch,
Crown of Madness,
Detect Magic,
Disguise Self,
Expeditious Retreat,
Fire Bolt,
Fog Cloud,
Knock,
Mage Hand,
Magic Missile,
Mirror Image,
Misty Step,
Poison Spray,
Prestidigitation,
Ray of Frost,
Ray of Sickness,
Scorching Ray,
Shield,
Shocking Grasp,
Thunderwave,
True Strike, all without material components.
If your party can't get out of jail with all of this at their disposal, let them sit another day and think about what they've done.