I'm running 8 to my box, 14 inside.unless you're giving those subs some HEAVY wattage, 12 gauge, hell 14, will be fine to wire your subs' voice coils to your amplifier.
Only when done correctly. 8 gauge to the bolts on my box, then splits to each coil. 8 for the total current, 14 for 1/2 current.I didnt know it was okay to mix them.