I wanted to come back after all this time and give an update. I’ve often thought about doing this but I always put it off, even though for my precious sister this has ended happily. Maybe this story will help someone else if they are ever searching for threads like this.
First off I want to thank everyone who contributed to the thread, each post was a blessing. Also for the posters who messaged me directly with offers of housing - thank you. I’m sorry I didn’t reply. I was up to my eyeballs and I knew we could house my sister between us. But thank you nonetheless. It was so good to feel heard and for the urgency of the situation to be recognised by others.
We got her out within a month of her confessing to me how bad it was. DSis amazed us by saying she wanted out by x date in September and we stuck to it. The advice re what to get out, on here and from the woman on the domestic abuse charity was invaluable. When he was at work, our other sister went round and they loaded up the car several times to get stuff out of the attic and home she would need. DSis was very anxious that he did not realise what was going on and we respected that. This was the beginning of realising how much of her life and energy had been taken up by ensuring he was happy. It was a complete eye opener - my feisty, opinionated sister was consumed by what he thought and was terrified of angering him. I had no idea that was the dynamic of the relationship but I realise now this is of course common in abusive relationships. We took birth certificates, passports, baby mementos, Christmas decorations without him realising.
She set a date to leave and the night she told him, my DF and DH were stationed outside the house as we were all scared he would become physically abusive as this was something the domestic abuse charity had indicated. DSis was absolutely against just leaving and taking the children without telling him first, although that is what we all wanted, as this would anger him. She also refused to leave the night she told him and insisted on staying. She slept in her DS’s bed with her DS that night as she said she knew her wouldn’t come for her if she did that. 
This was one of the scariest and most surreal points for us as her family. We stayed with my DPs and stayed awake texting her that night to ensure she was OK. Even though she knew how worried we her, that was preferable than angering him further.
She left to stay with my parents with her DC the next day. Some more things were removed with her ExPs knowledge, such as some furniture and household items. Our DF did this. There were many wobbles over the coming weeks and also many times he was manipulative and abusive. We are lucky she held firm, as much as I didn’t want to believe it, I know how close she came to returning. I also know if she had not had her family by her side every step of the way then she couldn’t have done it. His hold over her was so strong.
We are also lucky my parents could pay for excellent legal advice. I have a solicitor friend who put us in touch with an amazing colleague who handled DSis perfectly and it really helped her to hear someone outwith the family condemning his behaviour. Of course, he had begun telling her how weak her position was,how he needed 50% access to the children, that she owed him money etc, but our wonderful solicitor reassured her.
DSis would not disclose the sexual abuse to anyone other than me. I think he should be rotting in prison for that, but I have had to make peace with the fact that he will never suffer a single consequence for it. I am sorry if that is upsetting for anyone, it is upsetting for me too, but I get to see just how much better her life is now he no longer has the same hold on her, which does help me.
He made every step of the way difficult. He contested everything from money to access to debt. He wanted to be able to say “I’ll see the kids now” and drop them off whoever he liked. DSis needed a lot of support to advocate for herself and ensure she was no longer at his beck and call. But she has managed it.
My sister, her children and in turn us as those who love her are so lucky that she had a physical place to go, financial support and that we could provide unwavering support to her. My heart goes out to anyone trying to do this journey on their own. The words of the domestic abuse advisor helped me so much - this was her “first attempt to leave.” We are so grateful it only took one attempt for my sister. But those words made me realise how much strength and patience we would all need to get her out.