I did let the PCs of the game I am hosting receive too many treasures, so I would like them to lose at least some (or even all) of them. I thought about a simple ambush somewhere in the woods, where they would be stripped of their belongings.

But I have a hard time finding the right amount of bad guys, so the players won't feel cheated if I overpower the adversaries. The PCs should have a minimal chance of getting out of the ambush with their treasures.

The players' characters are like this:

• Angel-blooded Aasimar Cleric 5 (CR4)
  • Hireling Minotaur Skeleton Warrior 1 (CL7 - CR6)
• Human Rogue 5 (CR4)
• Dwarf Fighter 5 (CR4)
• Changeling Witch 5 (CR3)
• Human Inquisitor 5 (CR4)

I was thinking about a gang of bandits:

• 1 Human Fighter4 / Rogue6 (The leader of the bandits)
• 5 Human Rogues 3

The five rogues would be armed with heavy maces and longbows and hide in trees, whereas the leader has a heavy crossbow and a Scizore. In my mind it's some kind of Robin Hood setup.

Is this a setup that would give the players a tiny chance of winning? I do not want them to feel cheated. What kind and number of adversaries would you recommend?