2 Players in something really designed for 4-6...
I actually would cut the number of encounters, and I'd recommend a Cleric and a Rogue/Fighter (rogue taken first), if you don't have any more players. A "friendly NPC wizard" might not be a bad idea either. This makes 3 characters and much more doable. Also, when Shensen & the Striders others that could join the party are around, encourage actually letting them join the party.
Okay, the other thought is this: Gestalt. Cleric/Wizard and Fighter/Rogue. You could even do Rogue/Wizard and Fighter (or Barbarian or Ranger)/Cleric. It still will be a hard battle ahead, but it makes it a little more doable. Emphasize stealth here.
The third, and final suggestion is that both players play 2 characters each. I'd still go with letting the NPC's that can join the party, otherwise you'd be okay without them in this scenario.
good luck
/d
I think multiclassed PCs are a good idea.
Reduce the the level/HD of some of the foes.
Cut back on the number of bad guys.
Allow a NPC or two to tag along. I normally use a straight fighter or even a warrior(easy to run) and/or a cleric (focused on healing).
Animals companions (like a war dog or two) are really helpful at low levels.
When running small groups I liked having the PCs a level or two higher than the suggest levels.
I was recently playing in Shackled City by myself. It was quite easy. Had the four core classes all complimenting each other. Had the grand total of starting gold to use on all my characters. NO party in fighting but, my characters were keeping secrets from each other. Was a good time and combat went really quick. Approach your two players and see what they think. Was lot of fun always changing hats. Blasting with the mage, to then buff up the paladin, with the cleric, to powerattack some monster and then the thief to loot the body.
My feeling is that, instead of trying to make the bad guys weak - which means modifying every single encounter in the adventure instead make the players strong. In this case really strong. With only two players you don't have to concern yourself to much with party dynamics and balancing players against each other. These two should work together pretty well. Another good reason, besides that amount of work involved, to make the players strong as opposed to the bad guys weak - My bet is your players will love being really kick ass. On the other hand if you spent 10 hours before every session trying to make the bad guys weak you players would barely notice. Lots of work for little reward in my opinion.
While I prefer more down to earth gaming with a more 'traditional' party with only two players that is just not an option so I'd see this as an opportunity to play out a more high powered game.
Here is what I would do for a background.
Good will confront Evil on any battlefield anywhere at anytime. You are a living weapon, born for only one purpose - to destroy the Evil at the root of Cauldron.
Being the chosen weapon of good comes with benefits...
* Gesaults a great place to start. Get them to cover all the bases.
* Give them leadership for free at 6th level. Encourage both players to have at least above average Charisma.
* That should not be hard - point buy overkill... give them a whopping 36-40 point buy. Far far above even the greatest of normal mortals.
* Start them off at higher level. At least 3rd.
* Templates baby...who wants to be a normal human when you can be Half-Celestial or Half-Gold Dragon. allow them to take a potent template. Be a little careful here...Half-Celestial and Half-Draconic won't really break anything but something like Half-Vampiric is really something the game is not really made to handle in a player. Its better if the template gives the players more of things like hps, stats, AC, a little DR or SR never really hurts. What you don't want is ability's really out of left field like army summoning or something.
* Give them a few 'second chance' type items. Something like an amulet that will cast raise dead fully on them inside a allied church 3 times during their 'lives'. Is probably good.
* Grant them cool creature side kicks like dragons or celestial unicorns or something along these lines. I'd make it so that they essentially had leadership twice. I'd grant this at 4th level. So they have one level to learn their abilities then they add their animal side kicks abilities, then two levels later they add their henchmen. This should give them just barely enough time to get fairly comfortable with all their extra friends.
* Watch the experience carefully. I think that all these benefits might actually make them too powerful. In fact I'd charge a 1/2 share of XP for each of their henchmen and animal side kicks. That way they earn XP as a 4th level party while there are really 6 of them (but 4 are probably a little underpowered while 2 are overpowered).
* If their animal or henchmen die they get new ones. Encourage them not to abuse this however.
Why not just try to get some more players? Put up some signs at your local game store, look online, etc.
Your profile doesn't say where you are at Lupus980. That might be a place to start. I live in a moderately sized town and know of three games in play, and two FLGS with RPG nights recruiting players and DMs.
I'm sure you know someone who might want to try playing, so you could have a "newbie" play the fighter. It is an easy role to play and is fun, getting someone in all the action.