Controlling 2 AUX ports with a single 3-position switch

I’m new to the community and technology, so I apologize if the terms used are not the accurate ones.

I got a new Radiolink Pixhawk and loaded it with ArduRover fw v4.1.5 using MP v1.3.77.
My Pixhawk is connected to my ground station controller and everything works fine.

I want to program a 3-position switch (SW-1, RC Channel 5) to control a valve. The valve is connected to another 3rd-party controller, which requires 2 dry contacts to control it. Dry Contact A opens the valve, Dry Contact B closes the valve. If both dry contacts are opened, the valve is stopped.

I would like SW-1 to perform the following:

  • top-position closes dry contact A (opens the valve)
  • middle/trim position opens dry contact A and B (stop)
  • low-position closes dry contact B (closes the valve)

My idea was to assign RCIN5 (SW-1) to AUX1 and RCIN5 REVERSED to AUX2 (In MP’s Servo_Output Config).
On AUX1 and AUX2 outputs I would physically connect two 3.3V relays to trigger each dry contact.
When SW-1 shifts to TOP, AUX1_Relay would be triggered (closed).
When SW-1 shifts to TRIM/MIDDLE, AUX1 and AUX2 Relays are opened (valve stops)
When SW-1 shifts to LOW, AUX2_Relay would be triggered (closed), since AUX2 would get a reversed PWM signal.

However, the Reversed function is not working for RC signals (also read about it in various threads).

Would you have suggestion how I could implement this function?