What is the diet they have been on? Only reason I can think of rejection is improper diet or bred too young.... How old are they? Rejection in gliders doesnt happen often. Are we sure they are not related? Another reason for rejection is something is wrong with the babies. YOu may not see it, but they can tell. If they are related then that is a possiblity. At what STAGE are they rejecting?
As far as cage size it can vary depending who you talk to . If you are looking to go by standards to get a liscence I believe for a breeding pair the cage has to be ppretty big. 4X4 ft is what I was told a few years ago...I am blanking on what those people are called...the ones who give you the permit..sorry. However I have seen gliders living happily (or seems happy) in 2X2 bird cages.... brining up another possibility of rejection..what is thier cage size?
The bigger the better with these guys. They also need a pouch or nest box. Branches are a great plus. Not everyone uses lighting. Just a normal room light. And gliders seem to like a small night light by the cage at night. They are nocturnal so I shouldnt think they need any sunlight.
Fresh fruits, vegis and source of protien on a daily basis. Low citrus fruits are best. Apples and bananas are great. They also like grapes ALOT, but I was told by annother long time breeder that he thought that grapes MIGHT have a bad effect because of some research on dogs..dunno if it does or not. I never had problems, nor had he. It's just precautionary. Sweet potatoe, boiled chicken, hard boiled eggs, cat food, meal worms are all good sources of protien..just dont over do it. And only give nuts of any kind as ocasional treats. They can get fat easily which can lead to paralisis. and death. And lastly, a mixture of half water half juice (usually apple works best) mixed with HUMAN rice cereal BABY FOOD, mixed to about a yogurt texture, is GREAT extra minerals and vitamins especially or breeding pairs and weaning babies.
So questions to help you with your rejection problem are:
A: What size cage are they in?
B: At what stage are they being rejected?
C: What have they been getting fed?
D: Are you sure they are not related?
Hope to be of help