When it comes to single DVC subs, your wiring options are half of what the ohms are and double what the ohms are. For a DVC 1 for instance, if you wire parallel you'll end up with a .5 ohm load, and if you wire in series you'll end up with a 2 ohm load. DVC 2 would be 1 ohm for parallel and 4 ohms for series.
When it comes to 2 subwoofers, your options are 1/4 of what the ohm load is, the same as the ohm load, and 4x what it is. For two DVC1 ohm subs, if you wired in parallel parallel, you would see a .25 ohm load, if you wired in parallel series, you would see a 1 ohm load, and if you wired in series, series, you would see a 4 ohm load.
With DVC 2, parallel parallel would give you a .5 ohm load, parallel series would give you a 2 ohm load, and series series would give you an 8 ohm load.
Parallel is when you wire your positives together and your negatives together, series is where you wire a positive from one coil to the negative of the other coil, or when you wire the positive from 1 subwoofer to the negative of another subwoofer.
Hope this helps