Another Report said:There isn’t necessarily one Keyblade for the Dark side and one for the Light side, just as many as there exist people with qualified hearts. Concerning the conditions to wield one, at this stage, “Those with strong hearts” is the only obvious one. However, less obvious conditions still exist and there are still plans for an opportunity to reveal those. Riku’s “Way to the Dawn” and Kairi’s Keyblade are naturally the same type of Keyblade as Sora’s. However there is no particular explanation for the Soul Eater’s transfer and occurence, as well as Riku’s handing it to Kairi. When there isn’t a normal process of acquisition, I think it’s ok to think there is some deeper meaning there.
Yeah Lifes.Lover is correct.
Byronic Hero, I don't think Sora was Dual- Wielding during the Xemnas fight. He temporarily held Riku's Keyblade. It was the same situation as when Kairi and Leon held the Keyblade. It's not really Dual- Wielding in my opinion.
Edit: SufferingAngel beat me to it.