The remaining nestlings are honing their skills. Baby #2 will most likely be the next to branch out. That baby was "bouncing off the walls", so to speak, and did eventually get onto the side branch before descending back into the nest. Watching the efforts you realize how hard it is to get to the next stage of development. Alpha Baby has the confidence now. The remaining nestlings will get there. It could all happen very fast if the babies understand that from now on food is served out of the nest.