Idea! We have badass stealthy archer Heinrich with us. He peaks, and starts sending arrows from the cave bend at the slavers while we wait just around the bend. When they rush toward Heinrich, we intercept. Will certainly give us surprise bonus, as they won't expect three to be waiting at the ready right next to Heinrich out of sight.
Heinrich has all the stealth skills, so if he peaks and sees a clear path to advance, we could follow him, but non-sneaky me will surely alert them.