That is a lot of tail O.o
I can picture it in my head but must doodle some to sort it out....
Ok, first, you need a strong base to hold that much structure off away from your body. I think a very fitted belt made of something tough like denim would be a good start. It needs to go from your natural waist to a couple inches past your hip line (or just under the curve of your bum). Buy or make, doesn't matter, something that fits and covers like this: http://www.thevintagepeddler.com/cat...03/3823841.htm
Then I'd use 14 gauge wire to support the tails as well as make them poseable. I don't think I'd stuff them except maybe with balloons. If it were a single tail of that size stuff away, but at seven? the weight will be daunting.
The most comfortable way to wire an appendage is to give the wire a curved base (circular or oval or whatever, just no sharp corners) that sits flush against your body then angles away from your body. [think of those old fashioned spikes people used to use on counters for sorting receipts, wire coil at the bottom then the long straight bit sticking up]
sew this curved wire base to your support garment, then alter the skirt to go around it.
last, slide your tails over the wires & do a couple stitches through the material around the wire to hold them in place.