Here is some good information from www.thepetglider.com/pages/the-glider-nutrition-system
The sugar glider's high diet of fruits and vegetables contains inverse amounts of phosphorous to calcium. High phosphorus and low calcium leaches calcium from their bones making the bones brittle and easily broken or fractured. Calcium deficiency will make your glider sick, then will cause hind leg or total paralysis, and will kill them. If you notice any trembling or shaking (on a consistent basis, not just when scared), or any trouble climbing in the cage or hanging on to the perch, contact your exotic animal vet immediately. Neocalglucon or Calciquid (calcium glubionate in a sweet syrup), is an excellent product to rebuild calcium quickly, your vet (one who is very knowledgeable in sugar gliders) can instruct you on how much and how often to give this calcium supplement. Do not feed these high phosphorous foods: beef, most seeds, nuts and cottage cheese
Maybe its partial paralysis of the back legs, are you giving them any vitamins?