Ok, so it sounds like you have been on your own for a few days with the children and newborn which would be tough for anyone. It also sounds like you have done a good job so far holding the family together in a time of need. It's ok to cry and be overwhelmed by your emotions even if the children see you.
Let's look at you and work on your mental health @Sunnyside226:
Do you have a medication that you can take to help you prevent a meltdown? What supports do you have in place for your autism that you might be able to call on right now?
Looking after the children and newborn:
You have been on you own for a few days and it's ok to ask for help particularly when you have not done this before. I strongly encourage you to contact Parentline for a strategy to support you with the children: Parent Helpline | How Parentline Can Help You | Kids Helpline
Are you able to care for the children right now? I'm sure they will need dinner and start a bedtime routine shortly and are you prepared for that?
RiverSeal