Mama and grandma too!!!

Tl
Today I found out my son's girlfriend is also pregnant.  She's 18yo and he's 20yo. She's due on May 28, 2017 and I'm due May 29, 2017. He doesn't know that I'm pregnant just yet. I'm going to wait to tell him until after my first OB appointment. 
Neither decided to go to college. They both are working odd jobs. 
Am I wrong if I decide that she can't come live with me? I think they should get their own apartment. 
I can't afford to continue to take care of him.  I have a 13 yo diabetic type 1 daughter and my baby that I need to worry about. That's enough stress.