You will definitely need to run a power wire from the battery. 2 sub amps and one sub?
I would highly recommend you have a pro install this stuff. And I don't mean your friend who says he thinks can do it. I've seen some crazy ghetto installs before.
Run atleast a fused 4 gauge from the battery to a distribution block(4gauge to 2-8 gauges)I would wire each amp to each voice coil on the W7 sub.Should be a 3.5ohm load to each mono amp.Just make sure you "Y" the mono input to the amps.Hate to have the voice coils battling each other.Man,that will pound!W7s rule!