Why does Obito only have 6 reanimated jinchuriki when he fights with Naruto and Bee, I thought Obito got 1-7 and he said in the fight "6 against 2 is unfair" to Naruto im confused af.

episode 325 btw.
He has extracted the Bijuus with one to seven tails but the former Jinchuuriki of the Ichibi - Gaara - is still alive.
Another reason is that he is controlling them using the Six Paths of Pain 


  an Outer Path technique that allows a Rinnegan user to manipulate up to six bodies as though they are their own. 


Wiki