What temperature is your room reaching overnight? Also how do you know the snuggle safes are untouched?
I’m sorry you’re having a really stressful time with your girls right now, I know how worrying it is, especially when there’s no clear cause.
My boys live outside (in a garage), and we live in NE scotland so the highest the temperature has reached in the past month is 10-15 degrees. I actually bulk my boys up over winter, they get a little extra nuggets and a little extra veg during these months. I give my boys multiple options of heat pad, one snuggled under hay in one area (it’s best if it’s in an area where they can lay near the heat pad, but still in hay) and my old boy with arthritis gets one just sat in his cage and he loves to lie on it.
Do you provide a layer of hay in the areas where your girls sleep? I just wonder as most indoor cages don’t use hay as a bedding. As my boys are outdoors they have hay in every high use area and it’s a great insulator, even a layer under the tummies can be enough to keep the heat in, like a blanket/duvet for us. In the depths of winter I provide piles of hay, in which my boys can fully “submerge” themselves in hay, but I don’t imagine your girls will need that indoors.
Edit - I am also wondering how much does the temperature fluctuate from during the day with the heating on, to the early morning/overnight. This may not sound great, but atleast in my boys case they’re cold all the time so they know how to deal with it, whereas if your room is lovely and cozy during the day and then really cold, that can definitely have an affect on your girls.