Hello!
I saw this threat and I might actually be able to help you.
I used a pattern of Simplicity, to be exact I used this one: Simplicity 7417
But I worked to change the pattern quite a lot. First of all, don't use an elastic band for the underdress. It would look really weird if you want to add the wing to it. I simply added a couple of tucks and that did the job too!
You could also use a different pattern for the undergown if you feel like it. For the sleeves, I cut out squares and ruffled them.
For the blue gown, I cut the front part of the original pattern in two and added a little bit of "boob curve", and of course, the pointy front.
If you have more questions, feel free to message me!