I'm so stressed out, I told my mother that if she moves to the apartment above us, I'm going to move my family out.
Why would you want to move out of your apartment just because your mother moves into the one above you?
She's terrible, she'll be visiting us all the time and we won't have any distance between us.
You should talk about this with your family and your mother. You can't stop her from moving in, but try to set some ground rules so that all of you have the space you need.
I'll try but my mother does what she wants to do and doesn't care how it affects others.
This sounds like a good opportunity to improve your relationship with your mother. The two of you could resolve your differences and have a much better relationship going forward. Spend time talking and be open minded when you speak to her.