What is the functional difference between DSB and 2SB mixers, and why exactly would 2SB be better for radio astronomy?
Is the separation of the two SBs to two outputs the functional difference between 2SB and DSB? If not, what would it be?

Almost certainly yes, although it seems that the only hits that &quot;2SB mixer&quot; gets is for astronomy sites.  See the figure, from the first paper you cite.  It clearly shows two sidebands being received independently.
Basically, you're getting two SSB channels out of this, which, presumably, can be selected downstream.


The abstract of the second linked paper says that 2SB mixers' &quot;main advantages being to avoid spectral confusion and to diminish effective system temperature by a factor two with respect to double sideband (DSB) receivers.&quot; Is it possible explain in fairly simple terms what that is so?

Spectral confusion: DSB mixers take the sideband above the carrier and the sideband below the carrier and mix them equally to baseband.  The output of a DSB mixer is the sum of the downconverted USB and the downconverted LSB.  For uncorrelated signals, the power in the USB and the power in the LSB are added.
Noise temperature: Noise temperature is a function of the ratio of noise power to desired signal power.  Because the DSB mixer output power is the sum of the LSB and USB power, it's output has the noise contribution from both of these sidebands.  Because (based on the context of the article) the desired signal is in only one sideband, you're getting the noise power from two sidebands, and signal from one.
With a SSB mixer (remember you get two SSB channels out of the 2SB mixer) you get the noise power from one sideband, and the signal from one sideband.  So the power/noise ratio is doubled -- this results in the noise temperature being halved.