Chins staying on bottom of cage?

One of my chins has been losing wait and powdering her food. A visit to the vet led to xrays and what looked like the very beginning of a blockage, she was still digesting and passing food so they put her on antibiotics and gave her fluids and that seems to have resolved. My parents normally care for them while I'm at college but because of the health scare, I brought this bonded pair with me to take to the exotic vet at the vet school here (very well respected institution), as I want to be sure she is fine. As this is only temperary and I have vet bills about to hit, I wasn't up for spending a bunch on a second cage. At home, they have a double level Ferret Nation that wouldn't fit in my car with everything else even if I could get it back together when we got to school. I ended up finding one of the Super Pet my first home cages on craigslist for cheap and getting some new shelves, etc so that I don't have to lug things back and forth for them. I took our the plastic shelves that came with the cage and got it all decked out. They have plenty of places to go plus their favorite wall hut, tube, lounger and hammock are up top. They'll need more play time outside because the cage is smaller but I feel like they have plenty of room and things to do in there. The problem is that neither of them seem to want to leave the bottom of the cage. They have been taking turns on the wheel and the poo reveals that they went one shelf up for hay but it doesn't look like they are exploring upwards. I expected this from Lilly. She gets nervous climbing at times, I had to keep the ramp in their FN because she wouldn't change levels otherwise. But Cindy is my tree climber and even when she wasn't feeling well, she would head up and sleep in her tube. Just wondering if anyone has any suggestions on how to help them take advantage of the full space!