Amazing animals aren't they? Got that birth thing down to easy but carrying it around in the pouch can't always be too comfy.
They can have 3 on the go at different stages of development. They can suspend them from growing until conditions improve.
One as a fertilized egg, one at embryo stage (as in vid. but not yet birthed) and one feeding in the pouch. They have 2 teats each producing different types of milk so when times are good they can birth one while another is still at preweaning stage in the pouch. How the tiny ones don't get squashed is a wonder of nature but they can sure churn out the offspring in a good season.
I love to watch the Joeys staggering around and jumping about, going to miss that when I move. siiiigh.