Apron taxiways are just taxiways, except they are on the apron. They help planes on the apron connect to the main taxiways or the planes on the main taxiways connect to the apron.
I don't know what you meant by holding taxiways, but I assume you meant runway threshold or runway holding point. In that case, here's your illustration:
Notice how the apron ...
You wrote that
intuitively, one would expect that UHF-radio-wave-reflecting surfaces near your glideslope antenna would be a bad thing, due to the potential for multipath interference
However, multipath interference is exacly what we want here. The antenna is mounted a certain height above ground and the aircraft receives both the "line of sight" and "...
Source: FAA 6750.16E - Siting Criteria for Instrument Landing Systems
The more common G/S antenna type works by reflecting the signal off flat ground, called "image type".
A non-image type was not available in the 70s as it's a mid-90s invention (patent; IEEE).