If you reeeally want that length, be aware it will tangle very, VERY badly. That said, I recommend combining this: http://arda-wigs.com/products/delilah
and this: http://arda-wigs.com/products/jareth-long
to get the layers plus length. OR this from EpicCosplay
and one of their shorter wigs. Personally, I don't like the looks of EpicCosplay wigs, but I hear they tangle a bit less.
Also note that you WILL NOT be able to use the same wig(s) for both those characters. High ponytail wigs like that require special styling to look right, usually involving a short wig and a clip on ponytail or lots of cutting and glue. A long wig can not just be pulled up into a ponytail, and a wig specially made for high ponytails will not look right hanging straight down.