There is a HUGE difference between a joey that has been rejected and needs to be pulled and hand raised, and one that needs to be supplement fed because mom needs some help. Unless you start to see signs of rejection (bites or scratches on the joey, especially the face, the parents leaving them alone for long periods of time or leaving them outside of the nest, etc) I would not recommend pulling the joeys. A glider's parents can do a much better job of raising their young than we will ever be able to. With that said, it is of course possible that the babies will need to be supplement fed. If you find they are not gaining, but the parents are still caring for them, you DO NOT need to pull the joeys to supplement. You can offer them supplemental feedings during the day and night and still allow mom and dad to do most of the work. The best time to do this is when mom is already out and about during the evening to stretch her legs and eat.