Well, depending on how much the DM "cheats" (i.e. prepares the NPCs for your exact tactics), a few Ropes of Entanglement should slow down the spell caster for a moment (unless he has Freedom of Movement up). The idea is not to incapacitate him per se, the idea is to limit him to casting verbal only spells. And, if he attempts to get out of the rope, better still, he is wasting actions on that instead of casting spells. (note: a DM should not allow a caster to Dimension Door out of the rope, but some DMs do, so this might only take up a round of the wizard's time).
Ray spells are also your friend. Even high level opponents tend to have low touch ACs. After a Mage's Disjunction (if you can get that on scrolls, it is a 9th level spell after all), hit the Fighter with a Ray of Enfeeblement or Empowered Ray of Enfeeblement. There are also some good Ray spells in Spell Compendium, but I do not have that book at hand at the moment.
Acid Fog (probably on a scroll) followed by some type of hemisphere wall spell (Wall of Stone works well) might be good against the Fighter/Cleric. He will probably be buffed so that the Acid does not affect him (or, he might not), but it might take quite a few rounds for him to get out (assuming he has no type of teleport). It all depends on how many Dispel Magics he has prepared. But regardless, if you are slowing him down forcing him to cast Dispel Magic, he will not be attacking.
Course, just casting Solid Fog on him every time he either dispels the fog or whenever he steps out of it might be sufficient.
Once one of your Monks is near one of the NPCs, have the Cleric cast Silence on the Monk. Ditto for the other Monk near the other NPC. You have to do this before the Wizard can cast a Globe of Invulnerability. Then, have the Monks grapple.
Unfortunately, your party has only one mage and one cleric. There are not enough spell casters in the group to do real nasty combo stuff in a single round. Multi-round combos give the enemy a chance to dispel.
Your best strategy is to have the spell casting PCs concentrating on slowing down the NPCs while the rest of the PCs concentrate on taking one of them down (preferably the Wizard). Divide and Conquer.