My guess is he won't have anything to do with the eldest because she is old enough to be able to resist the mind games.
My ex did this, though it was nowhere as extreme as yours, as he is rather weak and silly. The DCs didn't know what was going on, they only knew that Mummy was being rather peculiar, and if they stayed with Daddy they could keep the house and (in the case of DS4, who was 9) be looked after - I spent most of the day at work and then collapsed in front of my PC in the evening, killing dragons as a form of stress relief/avoidance. For a short while they believed his story that I was leaving them all to live with a young lover, probably overseas. (The day he said to DS4 "How would you feel about having a younger daddy?", making the little fellow burst into tears, was the day I absolutely knew I was right to divorce him.) They soon realised that was rubbish; but they still couldn't understand why I was breaking up their happy home, as an awful lot of the emotional abuse took place between just the two of us, and the DCs were used to the frightful conditions we lived in and couldn't see how unacceptable it was. I plugged on with the divorce and forced the sale of the house, which was another cause of resentment (it was never realistic to keep it, he was just stringing them along of course). The older ones moved in with him, the youngest was supposed to spend a week with each of us by turns but kept begging to go to his dad's and made excuses to stay over etc. I thought I had lost them. It didn't help that I was struggling with depression and didn't feel I was a fit parent so they would be better off with their dad, who at least they were used to.
Two years later, though, it's a different story. Two of them live with me full time, the other two having their own lives now use my place as a base when needed, and they all avoid seeing him as much as possible, though they do pity him. The school actually asked me to take DS4 full time as they were worried about the effect living with his dad was having on him; the others are grown-up and made their own choices. I still kill too many dragons but nobody's starved yet.
Mind you I don't believe XH was evil, just a deeply insecure person so frightened of being on his own that he would do any underhand bastardy thing it took to ensure none of us left. (He could have tried being nice, but let's not be silly, eh?) He couldn't control me any more, but for a while he could control them, and justified it as "keeping the family together", uniting them all against me. It has been a difficult balancing act to explain this to them while at the same time not encouraging them to hate their own father. He loved them very much, he just had a bloody peculiar way of showing it.
DS4 (now a relaxed, intelligent teenager) said to me the other day "I didn't know what was going on; I thought you were the bad guy." I said I couldn't blame him at all for believing that, the way things looked, but am so so glad that he is with me now.
Chin up, it will almost certainly come right in the end, as you have official support. It will take a while to sort your poor DCs' confused little heads out after this treatment, though.