I had the symptoms you describe in one of mine around 3-4 weeks, and some crushed brewer's yeast tablets in the water or food do the trick. I just put a pinch of the powdered tablet into the night time water (they get a tupperware sort of container for their water, not a huge quantity.) Imprecise, I know. But, no more tremors.
With mine this was at the same time I started putting them outside during the day, and giving them greens and bugs. AND changing them to grower pellets instead of starter crumbles! So there was a lot going on and I was not sure which change made the difference.
I also had diarrhea in one of them, so I was not sure if they were fighting off some coccidia or what. But that's passed now too.