This one is pretty tough with multiple baddies with over 20hp so you are going to need 4-6 party members probably 2-4th level, but a weaker and creative party could do it. That said, if the baddies seem to powerful for your party, simply lower the HP and reduce the damage they can inflict (2d8 -> 2d6 or 2d4). Should work for any level with just a little tweaking.