Which aircraft are you trying to manipulate?
I know not many aircraft in the sim have reversing props.
Part of the problem here is that there isn’t a keybind for feathering. It seems, as you’ve noted, the reverse prop keybind is actually a feather keybind.
I know on the DC-6 for the reverse prop lever PMDG had to connect it to the water rudder keybind (if memory serves) since there wasn’t an actual one for reverse prop.