Post vet update:
Full MOT has been done. Luna is as I thought, fit has a fiddle. She's gained a little weight, gone up to 1025g, we're very happy.
Artemis' chest is now clear. No respiratory distress at all. Finishing the course of bactrim, but she sounds totally normal. The vet did see some slight sharp edges on her teeth, which made my heart leap into my chest, but he is not currently concerned, as her mouth looks fine and her appetite is extremely good. Her weight is coming up, today she is 795g, so she has gained 75gs since she arrived with us. She goes back in a month for another look. He urged me not to panic about her teeth, said as long as she gets plenty of hay they should be fine. I'm trying extremely hard not to freak out.