It looks like after you assign those two analogs as the software serial TxD and RxD you should jumper them to pins on the BT_RX and BT_TX header rows respectively.
In other words:
#define RxD 18 // (Arduino receives data on A4) --> BT_TX (BT Shield sends data on BT_TX)
#define TxD 19 // (Arduino sends data on A5) --> BT_RX (BT Shield receives data on BT_RX)
For more info on reusing analogs, see:
http://www.instructables.com/id/How-to-add-6-extra-pins-to-your-Arduino-with-no-ex/
I personally have never used analogs as software serial pins, but I have used them as digitals and they behave fine.
You do not want to connect the software serial analogs or the BT TX/RX pins to D0 & D1 because those are in use by USB/the Arduino IDE.
See the diagram on the wiki page for wiring info:
In looking at the schematics of both products in Eagle it appears that the Bluetooth shield is using ADC1 for its status bit and the touch screen is using ADC1 for X-. This could be why the touchscreen is misbehaving. If you turn off the status bit switch on the BT shield does it behave any better?