If you wire your subs up in parallel, each sub will have a load of 2ohms, when you wire them together in parallel it will then be 1ohm. Your amplifier isn't designed to handle that resistance. You will need to wire one voice coil to the other in series, and then each sub together in parallel.
Or change amplifier to one that handles 1ohm.
Or change amplifier to one that handles 1ohm.