First, regarding the datarefs, the standard dataref used for it is this one:
(it takes 3 values for Off/ Arm/Test modes).
Don't look at the old ../cockpit/.. datares - they are all "deprecated", only ../cockpit2/.. is actual.
The "sim/aircraft/..." section of datarefs is NOT used for controls, it's for aircraft model constants/features storing.
And, you don't need to bothering about standard datarefs (commands) - all them related to cockpit control are implemented it the SimVim data names already.
Yes, you need to use the SimVim parameter "Prop_AutoFeather" (for 2-pos) or "Prop_AF_Arm_Test" for 3-position toggle switch.
If it doesn't work as-is, you need to find the Carenado custom commands for this switch.
if Carenado has 3-position switch, it should be two up/dn commands, or 3 commands, if the switch is "simplified" (2 positions), it should be two up/dn commands or one "toggle' command.
(or one custom dataref)
Regarding the assignment of two parameters to one switch - simply add the next parameter in the configurator to the same switch ("Append").