I left my abusive ex.
It's really hard and you have to be clever.
I packed small things into my normal bags for the kids ( passports, marriage certificate, kids trust fund books, birth certificate etc) things I knew I would need I managed to get stuff in black bags I was desperate for, kids memory boxes and get them in the boot of my car ( that my mum bought me as he took my car off me, so he couldn't as my mum bought it me, I used to hide the keys in my boots and literally walk on them so he couldn't get them)
It took a good few weeks if it into months to plan. He was threatening to take the kids of me if I ever left saying I wouldn't get custody as he had me hook, line and sinker, everything was in his name ! I would walk with nothing. ( There is a reason why but I can't go into this, nor even being married entitled me to half )
It's a risk I had to try take.
One day he smashed up my belongings as I was talking to a friend on Fb ( male ) so that's the day I went. I said I needed to go to the shops.
I picked the kids up early from school and ran!
Never went back.
He did end up taking the kids, this is where I went wrong.
My advice is get her to the police, take her out the area so nobody sees you, get there advice. Woman's aid ring up, a bloody good DV solicitor lined up with court papers ready to serve in case he does take them. You can get an emergency hearing within 3 days if he takes them. Get free half hour solicitor can take you through getting safe contact in place protecting your friend and kids or no contact, they can help you judge that situation and a house be it crashing with someone, a housing association , family or shelter refuge place.
The above I didn't do. ( I did move in with family )
As much as I planned when he did take them I had to wait nearly a week to get in court as it fell on a weekend.
He told me he was going to commit suicide after I got the kids back. ....
I told him to get on with it, he only said it once. He told me he had cancer, he told me I would never meet anyone as good, he told me nobody would want me, he told me I was worthless, he turned everyone against me with lies.
It took years but now 1 DC has nothing to do with him. 2nd DC only sees him because he's his dad, a useless one at that.
I have an order now that he's not allowed anywhere near me.
It's really hard but it's sooo worth it!
Good luck