The pictures are from quite afar, hard to tell anything. The main question is what is different about the healthy plant? Other location? If so, is it a dryer or more humid location? Also the affected plants seem to be affected only on one side, as if something burned them.

Look like short of water.

Check the potting mix.

Thanks for the responses. There are four plants in a row, in containers on the south-facing side of my greenhouse. All have the same (adequate) water; see healthy one in second pic.

The symptoms remind me of early blight, or some type of necrosis; the developing fruit is so far unaffected. At this point I'm assuming I'm going to have to yank them, perhaps after seeing if the tomatoes on them ripen.

Early blight is certainly not. There's also suspicion of russet mites, but its too far away to tell. Just look at the stems of the affected branches and see if they have a slight sort of brownish tint to it (rusted).