Just when i thought it couldn't get any better... Anyway after Sparda lost his FE he obtained 2 pistols(idk what the time-line on this is) and created a sword Yamato to re seal the demonic world. As seen in DMC1 concept Sparda was only equipped with the Yamato and not the Rebellion(pretty obvious why he didn't trust humans with such an powerful sword that was used to open and close the Demon World). Anyway when before Sparda died he may have given orders to a close human friend to have the swords both sent to Eva to be given to Dante and Vergil so they won't be in bad hands. Since both swords contained demonic power then they would've both been sealed right along with the FE and Sparda's power.
O yeah just thought of something. Nero says to Berial "Fire's bad for my complection, I burn easily, never tan" Pale skin, another trait of being a relative of Sparda. He even says he "never tans" to prove this.