Alright, it looks like we don't have enough for a Metamagic Rod, but we can bring along 5 scrolls of Tenser's Floating Disk (4th level caster) no problem. We can reserve the rest of the party fund in case we win, or as a cash bonus for the PCs if they beat us.
So the current plan for silence is to put it on Armament, as he's good for charging in and wrecking up stuff. If we run into single sentries, we have armament grapple and pin them. If we think we need to be quick, Alistair can do nonlethal sneak attacks with a sap against the helpless target.
If we run into multiple sentries, well, then we probably just have our biggest damage dealers try to drop them fast - please TRY to keep a few above -10 so we can stabilize them, or better yet do the final blow with nonlethal if we aren't worried about the outcome of the fight.