The stern thruster will need a speed controller of its own. If you want to use the main 12v power supply then this speed controller will need to be another P93, set to Mode 2 (50% ESC). You could use the same two terminals of the P92 Distribution Board for both of the P93 units. Control of the stern thruster is via the Multiprop decoder using either K7 or K8 (rotary knobs) - see drawing 2.
If you want independent control of the main motors using the twin sticks then you should connect the red/black/white leads marked S and T from P94 to the two channels of the receiver which are operated by the two sticks. The P94's DIL switches should be set to Mode 1.
The motors rotate in opposite directions - hence the LH and RH props. Usually the starboard prop rotates clockwise when viewed from the rear, while the port prop rotates anticlockwise (both when going forward). You simply swap over the two wires between the speed controller and the motor to reverse its rotation, if necessary. UNDER NO CIRCUMSTANCES should you reverse the power connections!
I would strongly advise you to instal and connect the units one at a time, checking your wiring and testing each circuit as you go. If you suddenly hit a problem then you will know it's the last unit you connected that's the cause. There's nowt worse than wiring up a complicated set-up like this, only to find that you have a short somewhere. Ask me how I know................
Good luck; this is a very complex model.
Dave M