she will simmer down might take her a few more days though lol.
It's not an uncommon situation unfortunately.
If they are siblings, this young, if they have bred, they will probably dispose of any joeys before you are even aware she had any.
it's not uncommon for first time parents to cannibalize babies, the risk gets higher of it happening if something is wrong with the babies.
And sometimes the pair are super parents right out of the gate, even with oops babies ( oops babies are inbred babies )
There is no way to know how it's going to go, all you can do is be aware and prepared... def get him neutered which you already have an appointment for sounds like... really that is the most responsible thing you can do for them right now.
You basically inherited whatever the consequences are for someone else's choice to not neuter him sooner or in the very least separate the siblings before he was sexually mature. It happens a lot with gliders. Most of the time due to neuters being so expensive in some areas.