Lumen, don't forget that the thematic location is part of the thematic area.
Some people have posted about not being able to find the "two others" in the grid. My interpretation of the preamble is that the CLUES contain references associated with the 12 members of the group, and also references associated with two others NOT in the group, i.e. not included in the grid because they aren't found in the thematic location. (Having said that, I can find only one of the two other references, but two references in different clues to the same group member... D'oh!)
Thanks once again to all who posted hints here. I had a bad case of "parsing tunnel vision" with quite a few clues which wasn't resolved by leaving the puzzle a few days and going back to it.
Does anyone know what happens when Christmas Day falls on a Saturday, as it does this year? Is there no Listener that week — meaning there are only 51 puzzles in 2021 — or is it published on another day? (Asking for a friend...)