Low natural light is lovely and most desirable for many, however it can be quite challenging. I am not familiar with the K-30/50 or the K-3, but the K-5/II/IIs seem to have good high ISO, and a raw editing program can help with noise reduction. The second image you chose centre weighted metering, probably a good choice over pattern metering as has been my experience with a K-5. With lenses for low light we need wide aperture lenses, fast lenses ie f2.8 to say f1.4 or 1.2 or faster. I consider f2.8 to be moderately fast, and then we need them to be sharp wide open, or many people do. As lenses have different characteristics some research is usually needed, some are not sharp wide open and need to be stopped down a little, or some produce a nice softness wide open, they are all different. You mentioned the DA 31, is that in fact the FA 31, if so I would say use that one, maybe from 1.8, perhaps at f2, using a wider aperture gives less depth of field, but it can also blur distracting backgrounds and make the subject shine.
That brings us to exposure, try on manual, centre weighted, and keep the ISO down as far as possible and as always keeping the shutter fast enough not to cause camera shake, so for the 31 I'd keep it 1/50th or better maybe just a little more, say 1/125. Maybe some experimenting is needed as far as exposure goes, and it can easily be not easy to nail the focus with shallow depth of field, hence why testing our equipment is a good idea, then we can find out if we have any front or back focus issues with a given lens.
Raw is the way to go, instead of producing smaller jpg's in-camera, with a raw editor we have much latitude with adjustments to exposure and a lot more. Why go to the trouble of capturing an image, dear to you, and then have the camera throw out a heap of pixels in the compression as it makes a jpg? When a jpg is needed, can always save one from the raw editor.
Anyway some stuff to ponder, hope it helps and I reckon when you sort out this one you'll be ready to upgrade