If the main cable from the battery is large enough to handle the current draw of both amps, you can just get a distribution block and split it into 2. gound both amps at the same point. run appropriate RCA's for each amp and you should be good to go.
Yes the pre amps from your head unit go to the amps using the RCA cables. If you only have one set of pre amps on your head unit, you can use Y rca connectors by your amps. You can get them at radio shack, wal-mart, just about anywhere that sells RCA cable.