What is that Sound?
This sound is a greeting or happy noise.
Combination of Sounds
When you hear the combinations of sounds like in the video from your females, you are hearing that they are in heat and calling for a mate.
They are communicating with each other. It is also a way for them to say 'Hey where are my people?'
This is a scary noise to those not prepared for it. It is telling you that it is scared and/or angry about something. Many may do this the first few times you handle or as you get to know your new fur baby just because they haven't gotten to know you yet.
This sound seems to be a sweet sound as if the momma sugar glider is trying to comfort their babies. In reality they are trying to knock the babies off the teat as if to say you have had enough.