This site has excellent information about joey developments, it lists weights, general stats, and amount of time you can handle the joeys after being OOP:
www.petsugargliders.com/sggrowth.php
The "strangest sound" you heard is probably mommy singing to her babies, each glider is different, and will her own song, but here is an example:
www.youtube.com/watch?v=wXzDLxeYIi4
You should not force weaning, joeys are usually weaned after 8 weeks OOP, but it is appropriate to leave them with their parents until they are 10 weeks OOP. And you should have all males neutered before they are 4 months old. If you are planning to keep the dad intact, then you should separate the females before they reach 4 months as well.
Hope this is helpful.