Can Sil Leave With Her Own Kids?

Location: CO

I'm posting on behalf of my SIL. She is in a dangerous situation with her husband. He is violent, and she has been trying to plan an escape. He threatened divorce, and she was on board. She said she started looking for attorneys, but doesn't have one yet. When he found that out he "changed his mind" and wants to do counseling. She does not, and feels it's a power play.

Tonight, she called and said she thinks he's going to off her. We advised her to gtfo with her children. She told us she can't leave the house, let alone the state, with them because he made her sign a contract of some sort agreeing to those terms.

A divorce has not been filed.

They have not met with a judge.

There is no custody arrangements as they are both the natural parents, and, again, are not divorced. They still live in the same home even.

My questions are:

1. Unless a judge has ordered a custody agreement, she is absolutely the custodial parent and can leave whenever she pleases with her children, right?

2. Let's say she signed a document/contract he had a lawyer draw up, how legally binding is that really? (I know it's vague and a lot of contracts have to be reviewed to determine the validity, but I don't know the details.)

3. Is there any situation outside a judge issuing an order in which she could not legally take her children and flee?

Her biggest worry is facing consequences that ultimately take her children away from her.

(I don't believe she would be facing legal issues for taking her own children elsewhere as there is no ongoing custody battle and no judge-signed orders.)