We're going to extend the piezo wires and also attach a pull-down resistor.
Start with one piezo and trim the black wire a little shorter than the red wire. Slide on a piece of heat shrink tubing and strip the end of the wire.
Wrap the wire end around one of the resistor's leads (doesn't matter which one), and situate the two in the grasp of your third hand tool.
Strip one end on a piece of wire, and wrap this end around the same resistor lead. Solder the two wires to the resistor lead.
Now it's time for the other wire-- wrap the piezo's red wire and the other wire around the other side of the resistor, remembering to add a piece of heat shrink tubing before soldering.
Use a heat gun to shrink both pieces of heat shrink and repeat this process for the three other piezos.
Solder all the piezo's black wires to ground.