Koume and Kotake are collectively referred to as the Twinrova Sisters and are a pair of Gerudo witches. They are both the surrogate mothers of the Gerudo King Ganondorf, being somewhat his more devoted servants. They can brainwash others to serve Ganondorf (they do so to Nabooru in the Spirit Temple of Ocarina of Time) and merge to form the stronger witch Twinrova. The brooms the sisters use to fly become scepters through which Twinrova channels her power. They portray the same characters in The Legend of Zelda: Majora's Mask, though they are more benevolent than their Ocarina of Time counterparts. They are also found in a potion shop in The Legend of Zelda: Majora's Mask, from which you must save Koume in the Lost Woods. In Oracle of Seasons and Oracle of Ages, the Evil Gerudo Witches Twinrova enact a plot to resurrect Ganon.
Source: Wikipedia, "Characters in The Legend of Zelda series," available under the CC-BY-SA License.