In the evening after introducing them to their new tank, I found all four newts in the water. I wasn't sure how aquatic they'd turn out to be, but they seem quite comfortable in the water, and they're good swimmers. The water temperature was 12C/54F, and they were quite active at that temperature. The next morning, they'd retreated to their burrows in the coconut fibre land area at the back of the tank. The cloudiness in the water is due to a pinch of dolomite (limestone) flour that I added to the water earlier in the day to increase the mineral content and carbonate hardness. The tap water here comes from an upland peat moor, so it's extremely soft and very slightly acidic.
These were sold simply as Black knobby newts, but I think 2 of them were T. wenxianensis and the other 2 were T. asperrimus. Unfortunately, one of the maybe-wenxianensis died within 24 hours of arrival, but the other 3 seem to be doing fine. When I identified the other two as maybe-asperrimus, a Vietnamese species, I moved them inside where they'd have warmer temperatures than in the tank in my greenhouse that I started them off in.