I have a friend who has a very abusive alcoholic father.
In her early 20s, she decided she wanted to build bridges with him. She tried, and the first few meetings went well, then it deteriorated from there, when his true colours came shining through. (Not turning up to planned meetings, turning up drunk, abusive phone calls.)
She tried again a couple of years later, with the same result, and decided to call it a day.
Her mother was very much against her doing this. Obviously (in hindsight) she was pretty sure of what the outcome would be. But my friend had to do it for herself.
I remember her being so pleased to be reaching out to her father, so sure it was the right thing to do, each time.
So I have a lot of sympathy for your eldest DD. I can see she is probably hoping that it will all be lovely, and everyone can just get along nicely. She possibly feels a bit of pressure from other family and friends to produce two parents, on the day. Most brides do, after all.
But, it really is a very difficult situation for you. Hopefully you can talk about it properly with her, soon.