Oh that's super simple
Dolce & Gabana skirst are made 2 similar ways. 1st one (grey) is made out of a stripe gathered at the top. Or more like "gathered with pleats" but some of the pleats are left open. Sorry I find it diffcoult to explain in english
The blue skirt is made also with a stripe gathered at the top but that's not all. At the waist there must be a zipper somewere, because the top part of the skirt is a part of a circle (almost full circle). That's why it's so neat and flat.
And to the circle there is attached a gathered stripe.
If you want the skirt to look more like a bulb than like a bell the stripe shouldn't be just a rectangle. D&G used more like an arc. So the skirt is a small part of a very big circle sewn up with the top part (the smaller circle) with the longer sides together...?
Thanks to that the circut of the skirt at the bottom is smaller than in the middle.
Hope it's understandable
And those keep their shape with a tulle or organza petticoat. I'm sure about that. (tulle petti is lighter and easier to make but it can sometimes damage any delicate fabric like silk or your pantyhose)
Erin Fetherson skirt is made out of 14 panels and is held up with a short crinoline.
The panels are long trapezoids.
There is one thing about those trapezoids that's hard to acomplish. If you used normal trapezoids (not necessairly 14
) you would get a very triangular shape of your skirt. To make it a bell-like you have to change the geometry of the trapezoids. You have to change both of the longest sides of it into arcs. So its a bit wider in the middle.
To make such skirt it's best to take your crinoline, put it on a dress form and make yourself a pattern by pining some cheap fabric on it untill you get something nice fitting.
Better to take some thicker fabric for any skirt that's supposed to be worn with crinoline. Otherwise all the wires and seams will be wisible from underneath.
Well good luck!
And I'd love to see your results! (hope you'll post them)