They aren't.
Master xehanort and master eraqus hope this helps!
Because Of Xemnas' (aka. New Xehanort, Master Xehanort) Obsession Over the X-Blade
Xehanort's heart was once destroyed by Heartless but is now free, and his Nobody has been destroyed. Now both halves shall return to the whole, which means Master Xehanort shall return.
Terra is the villian, master xehanort we learn is sora in the future. He likes the name xehanort because " It makes him feel like a badass", so he says in the game ;) By the way, there NO, and i repeat. NO KINGDOM HEARTS 3, THE GAME IS CALLED BIRTH BY SLEEP
**SPOILER WARNING** Terra is sent out to find Master Xehanort and the source of the Unverse under orders from Master Eraqus. In the process, he is manipulated into doing terrible things by many people. This manipulated into killing Master Eraqus, and he leaves the Land of Departure unprotected for Master Xehanort to destroy. He then confronts Master Xehanort and fights him in The Keyblade Graveyard. After Vanitas creates the x-blade, Master Xehanort stabs himself with the keyblade and forces his heart into Terra's body. Master Xehanort manages to take over Terra's body, but Terra wont accept it. His armor rises from his will and soul, and attempts to reclaim his body. He manages to defeat Master Xehanort, but after the x-blade shattered, the body was lost in the confusion, and the armor-known as Lingering Sentiment- remained in the Keyblade Graveyard. Afterwords, Aqua confronts 'Terranort' (Master Xehanort possessing Terra's body) in Radiant Garden, and she tries to reclaim his body. In the end of the fight, Terra tries to eject Master Xehanort from his body by stabbing himself with the keyblade. This opens a dark portal which Terranort begins to fall into. Aqua rescues him, but is lost in the darkness, and Terranort is left knocked out in Radiant Garden. Braig then brings Ansem the Wise to see the knocked out man, and Ansem the Wise adopts the man as an apprentice. Ever since then, he's been called Xehanort, and has been the main villain of the series up until now. (Mind blowing, right?)
its master Xehanort
His body is taken over by Master Xehanort.
The one we know of as "Ansem" is Xehanort's Heartless. He shares some characteristics, such as obvious similarities in clothes, but is very different in appearance.
probably about 60 or 50
That would be Master Xehanort, a master of the keyblade who goes missing with his partner, Vanitas.
Beginning... A long time ago, there was a keyblade war between the forces of light and dark. It was believed that the war was fight in order to create the X-Blade, a weapon only created when a force of darkness crosses an equal force of light. Later... Master Xehanort, a keyblade Master, apprenticed a young keyblade wielder named Ventus (Ven). Master Xehanort had an ambition to control the powers of Darkness and thought that, upon obtaining the X-Blade, he could do so. Master Xehanort thought that Ventus, because he was a being of light, would be able to (involuntarily) assist him with achieving his plan. Eventually, Master Xehanort extracted a dark enitity from Ventus, which was named Vanitus, in hopes that the two of them could "create" the X-Blade. Unfortunately, Ventus's memories were erased, so Master Xehanort "dropped him off" with Master Eraqus, the keyblade master who teaches both Terra and Aqua.
SPOILERSAnsem is a scientist who's later known as DiZ. The real Ansem never became a Heartless. Xehanort is Ansem's apprentice and first experiment. Xehanort later named himself Ansem when Xehanort became a Heartless.Xemnas is Ansem's Nobody.So there are two Ansem's (the imposter Xehanort and the real one named DiZ).DiZ uses Darkness, while Xemnas uses Nothingness.Ansem (Xehanort) and Xemnas are two halves of Xehanort.