Hi Cat, I think you have done what you can for now. Just have to wait for the plants to get their vigor back in Spring. As I have earlier suggested, just a little more light would help them, since winter conditions really have much lower light and in a north facing window much lesser too.
The plant that you call Sister, may be due for a repot, since it has been sitting on same soil for 5 years, oftentimes, salt has built up in there and either you totally give it a good flush of water or consider repotting by Spring time, to improve the media. And if you plan to do that, you can also repot the one that looks like an umbrella plant.
My only suggestion for the leaves, is a real thorough shower wash outdoors when temps are better in Spring. Some would use a little soapy water or some very diluted lemon juice to clean the leaves by wiping them off. If you have time you can do it that way, or just wait for Spring to wash the leaves outdoors early in the day so it will dry out nicely before nightfall.
