Make sure you have the patched game (version 2.01), else you'll encounter some unpleasant things like enemies getting a free attack when your monk attacks them with fists.
Since you're playing a party pregenerated by the developers it definitely should be (and is) possible to beat the game with it.
For deciding who has to handle the traps I'd just look at the character names.
With the search skill you find them, with the disable device skill you disarm them.
Keep in mind that in IWD2 you have a lot of freedom to develop (and mess up) your characters as they level up. I'll give you some advice for this.
The weak point about the party is that you don't have a priest to cast the powerful cleric spells, but this can be changed.
At the next level up I'd switch the party leader (the Watcher) to priest and take only priest levels afterwards to get access to cleric spells. Even 1 paladin level is enough to get proficient with almost all weapons, the charisma based saving throw bonus and the paladin dialogue options.
Raise only WIS at level up for spellcasting, if you decide to stay a pure paladin or multiclass with fighter instead raise only STR.
You don't need a pure rogue to handle the thieving skills, so you can multiclass your gnome with illusionist (favored class for gnomes) at the next level ups for more casting power (with low strength backstabbing won't be very effective anyway). Rogue1/illusionist x is sufficient to handle the thieving skills until the end of the game, you can add maybe a 2nd and 3rd rogue level later in the game if you want, but caster levels yield more power.
When levelling up as illusionist pump up the spellcraft skill for successful scroll scribing and put the rest into search, disable device and open locks. Raise only int at level up for spellcasting.
Keep your druid pure class to get the powerful high level spells fast. At level up I'd raise DEX to 13 for being able to take the very powerful rapid shot feat. Afterwards I'd pump up WIS for better spellcasting. If you raise spellcraft to 10 you can take the "scion of storms" feat at level 9 to improve the damage dealt with call lightning and static charge by 20 percent. If you want to take a spell focus consider that most druid spells are transmutation spells.
Keep your monk pure class. Multiclassing destroys their unarmed attack skill. I'd raise WIS at level up, but STR, DEX and CON are also useful.
Take the "rapid shot" feat for a free extra ranged attack per round.
Keep your bard pure class and don't underestimate the power of bard songs. I'd raise only CHA at level up for better spellcasting and diplomacy, you can also raise CON instead for more hitpoints.
Keep your mage pure and raise only INT at level up. Spellcraft is checked for successful scroll scribing.
About feats (you get one every 3 levels):
"Improved initiative" doesn't work, so don't take it.
The extra +1 AC for "dodge" is useful for everyone who can take it.
If you want your party to move faster give "dash" to everyone (except the monk who gets extra speed anyway), later in the game "improved critical" is quite powerful.