How very sad and concerning .
What brought about this adoption?
Are either bio parents mentally ill? Was there possible drug use or alcohol during the pregnancy?
Right off the top…when she threatens to kill you, you should call the police. Period.
Make sure you keep your valuables locked up and consider a lock on your bedroom door.
If there is an opportunity for group therapy…I would explore this.
This sounds very very severe. Take good care of yourselves.