The entire fleet qualified for McMurdo seems to be six planes and three helicopters, if I'm reading this right.

https://www.usap.gov/sciencesupport/scienceplanningsummaries...

I would guess it to be pretty rare that multiple aircraft would be on approach at once, and if so, I'd imagine one could hold at a distance to allow approaches to be serialized.

There are a few other airports that have this, and my understanding is that only one aircraft can do the approach at a time. If another plane tunes in the ILS they will see the localizer and glideslope indications for the other plane.

I’m not sure how the TLS figures out what transponder to look at, I guess either the controller enters in the code of the plane on approach or there’s some reserved transponder code for the approach.

I would expect that these runways are not high volume. Temporary/shifting/special needs.

In theory, you can broadcast different signals on different frequencies, one per aircraft.