https://imgur.com/a/oEQDz

As you can see from the picture, the PFD is showing SINGLE CH even though both CMD A and CMD B are active, and both VOR/LOC and GS are captured. Why is that? I have both VORs tuned correctly to the ILS frequency, and set the HGS up too, not that it should affect the autopilots. 

If you continued the approach I imagine you got your answer. 

SINGLE CH is your indication that only one autopilot channel is active,  even if you have both selected.   At around 1200ft, if both autopilots are selected, I believe they conduct a brief self test and if successful,  SINGLE CH will change to CMD, and Flare mode will arm (white annunciation below the GS in the flight mode annunciatior).  Well,  that's if you're using Fail Passive mode; I don't remember what Fail Operational annunciates.

Keep flying.  The fact that both A and B are lit means both A/P are in the game. However, you will not see autoland annunciation until after the system check about 1800 AGL and you reach about 1500 when things should display as you expect.

I'd like to point out that almost all my ILS approaches are with single NAV and single A/P because I am not going to use autoland.  Autoland is for those very low minimums CAT III approaches and before you let the airplane land itself there are usually things ATC needs to make sure happen such as aircraft not taxiing into certain places.  I might do one CATIII a winter depending on where I fly.

Thanks folks.