It is possible to use multiple units with Picolog and therefore you will be able to measure 12 points.
However, when you say at the same time, this will ne be quite the case. To take a temperature measurement from each channel it has a 200ms converstion time for each channel and 200 ms for cold junction compensation, so to cycle through 6 channels on each unit it would take approximately 1400ms.
The TC-08's can be connected to a USB to serial port adapter and used in the normal way, but the USB to serial port adapter must be able to provide the power to the TC-08 so that it can run. The voltage level should be 7 volts on the positive and negative rail. This is all explained in the help manual, just follow the download button if you do not already have it.