Well there are a few ways to get the 2 subs to run @ 2ohms. If you are running 1 amplifier to each of the subs and each sub has a dual voice coil (DVC) that are 4ohms+4ohms, you simply run the wires in parallel to the 2 coils on the back of each speaker. If you are running the 2 subs from one amp, wire the 2 subs in parallel and the end result will be 2ohms.

(R1*R2)/(R1+R2)
(4*4)/(4+4)
(16)/(8)
=2ohms