Scared out of my mind!

I am almost 31 weeks pregnant with twins and have a 19-month-old son. My husband is a great support but works a lot so I’m pretty much on my own when it comes to taking care of my son as it is. I’m scared out of my mind for when the twins get here and how in the world I will manage newborns with a toddler. My mom will be here right after the birth, but only for a month or so and then I’m truly on my own for the most part. Are there any moms of 3 under 2 or in similar situations that have some words of advice? Thanks in advance!