Sachsen 750mm Braking System

I've recently come back from a few days looking at the lovely 750mm steam in Saxony. My lack of German meant I couldn't get some answers about braking systems I was unable to figure out for myself.

I believe vacuum brakes were the norm on these lines for some time but that air brakes came into use at some point.

So, at somewhere like the Fichtelbergbahn with VIIK locos, it seems the air braked locos haul air braked coaches. Is this correct?

But at the preserved lines (Schönheide and Pressnitztalbahn) operating IVK Meyers I assume vacuum brakes are still in use? But the bit I am uncertain about is where seemingly air braked locos are being operated on what would otherwise be vacuum brakes stock. So, take the Pressnitztalbahn where a IVK Meyer was in use alongside a VIK which very clearly had air brakes. Would I be right to assume the VIK is an air brakes loco with vacuum capabilities so it can haul vacuum fitted vehicles and (presumably) there is a proportional valve or valves which applies both braking systems at the same time through the use of only one drivers brake valve? And are the coaches on these lines dual braked or single brake system only?

Thanks in advance for answers!