The animators screwed up with the filler... Yuukimaru was not a jinchuuriki and they didn't explain how he could control the sanbi because even they couldn't explain it without saying he is one. Besides, the animators can't exactly show the sanbi jinchuuriki until he appears in the manga or if Kishimoto gives them the okay to use him if he has no use for him in the manga. By the way it looks in the anime, the animators didn't get the okay and had to base Yuukimaru off the jinchuuriki....It was poorly planned.
As for the real jinchuuriki, he likely died a long time ago if the three-tails is free. It could be possible the jinchuuriki didn't have the strength to control it.