Yes. Riku first weilds the Soul Eater, followed by the Keyblade of people's hearts, followed by The Way to the Dawn.
well technically, Sora's Keyblade is Rikus, as Terra chose Riku, not Sora. Sora was given it as Riku gave into the Darkness. The reason his sword became a Keyblade is as he was no longer evil and could now wield a keyblade
Because it was his understanding that Sora and Riku were the only wielders of the Keyblade.
Riku gets the Darkness Keyblade in Kingdom Hearts, made purely out of his Darkness. He loses ability to wield a Keyblade for a while, then he gets the Soul Eater Keyblade in either the beginning of Chain of Memories or the end of Kingdom Hearts, I'm not sure which. He get's Way To The Dawn after choosing the Path To Dawn at the end of CoM, or RE: CoM. Those are his only three keyblades.
Riku was supposed to be the Keyblade Weilder, but he had darkness in his heart.
The keyblade chooses the keyblade master, the Kingdom Key chose Sora, Way to the Dawn chose Riku, but only Kairi's keyblade didn't, Riku gave her the keyblade
Riku can use a Keyblade as he is Terra's chosen processor Kairi can as she is a Princess of Light.
Yes, Sora is a chosen keyblade master. He is the main Keyblade wielder, the second being King Mickey. Sora was chosen to be the keyblade master because of his powerful heart and strength. SPOILER****************** Terra wanted Riku to be the keyblade master, but Sora's heart was more powerful, thus Sora was able to combine his heart with Ven, allowing him to wield any keyblade.
You can not phisically use Riku's "Way to the Dawn", but in the final battle with Xemnas Riku lends Sora his keyblade to finish Xemnas off.
Because his heart is strong and pure!^_^The keyblade originally chose Riku and Sora was supposed deliver it to him, but Riku's weak heart gave into darkness, so the keyblade chose Sora as its master.
Riku is seen with the Dark Keyblade when Sora talks to him in Hollow Bastion in the original Kingdom Hearts game. However, Riku changes it when Sora fights him.
Riku's sword, Soul Eater, and his keyblade, Way to the Dawn, are not obtainable in Kingdom Hearts Re:Coded.
Yes, Terra choose Riku as his successor.