seems like youre talking about a lot of different things here, so ill cover all of it.

SIGNAL SOURCE:

the audio signal (the "music") is carried via RCA cables from your deck to the amplifier. RCA cables have a protruding center piece surrounded by a circular ground. they come in pairs as (most) audio is in stereo (one right and one left channel). if your headunit has only one set of RCA outputs, its OK to use an RCA splitter to deliver the signal to two amps. you can pick those up at any electronics shop.

REMOTE (REM) WIRE:

the remote wire is used to tell the amps when to turn on. a small (12v, around .1-.25amp) signal is sent through this wire to activate a relay inside the amplifier(s) to allow power from the main connections to the battery and ground to flow. although typically not fused, its a good idea to put a small (1amp) fuse inline with this wire as close to the headunit as possible.

---------side note--------
assuming that the remote wire remains the same guage throughout the install, its ok to "piggyback" it from amp to amp. however...if you keep adding amplifiers the remote wire might not be able to activate all of them due to the relitivly small signal it sends. in that case, you will need to add a relay and a bit of extra wiring to compensate. with only two amps, thats of no real concern to you at all.
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POWER WIRE:

as aaron mentioned, you should never really go lower than an 8ga (guage) main wire. in your case, a 4ga would work well from the battery (fused at the battery with a 60-100amp fuse) to a distrobution block. at the distrobution block, you have a few choices. as mentioned earlier, theres no need to add any fusing if the guage remains the same throughout the electrical path. assuming you wanted to split the (main) 4ga wire via a distrobution block to two(2) seperate 4ga wires (one for each amp), you would not need to add any extra fuses. you could simply use a non-fused distrobution block. however, if you were to run the (main) 4ga wire to a distrobution block where it split into two(2) 8ga wires, you would need to fuse each of the 8ga wires with 40amp fuses before connecting them to each amp.

for more detailed info, visit http://www.bcae1.com/ and click on the "fuses" section, loced at around 1/5th of the way down on the right side of the screen.

GROUNDS:

grounding is a hugly overignored problem in most car audio systems, but is very important. the ground is in a way the "valve" to let electrons flow through the amplification "parts" of the amplifier. imagine an amplifier as a garden hose, with the spicket being the power source, and the tip of the hose as the ground. as power (water) flows through the amp (hose), it fights against the resistence of the walls of the hose (or wire) and flows easily though it...assuming there are no blockages. however...if you place resistance (a thumb) over the end of the hose, the power (water) goes everywhere in search of a way to "get out". you always want to have the electrons (water) flowing as smoothly as possible.

to do so, you need to make sure the ground wire is at least the same size as the power wire connected to the amp, and that the ground is connected securly to a clean and unpainted piece of metal that attaches to the frame (or anywhere where theres a low resistence to make a ground connection back to the battery).

once again, for more detailed info, visit http://www.bcae1.com/ and click on the link entitled "vehical chassis ground", which is around 1/2 way down the right side menu.

:shhh: i do cocaine :/shhh: