I agree a paternity test is of the utmost importance.
Another reason NOT to move her in with you.
You might be the wealthiest man she was having sex with rather than the only one. That would be a clever trick for her to have you paying for & raising another man's child if she were to pull it off. Until these questions are answered (AFTER the birth) do NOT turn your 9 year old's life to crap by moving her in.
Obviously she has worn you down. You are afraid of this woman's wrath when your #1 concern ought to be the emotional wellbeing of your 9 year old. Don't be a bad dad to the kid you already have. Read that again.
This woman does NOT care about your 9 year old. She cares about herself, your money, the baby, her 9 year old, you, & your 9 year old IN THAT DESCENDING ORDER.
Tell her to move nearby but not into your home. If she is understanding and agreeable to do that at her own expense then I withdraw my opinion expressed in the above paragraph.
Tell her you have reconsidered the moving in because you are concerned about your 9 year old.
Your kid is supposed to be your top priority. Stop being an ass hat to the kid you already have. Time to step up to the plate dad.