Sasuke will light em up 
Seriously though, Amaterasu spam is key to take down the Bijuu. Kakashi can also rip a couple heads off too. Obito will more than likely not attack since its chakra taxing controlling the Bijuu.
Kakashi can hold off Rinnegan Obito, he won't get caught by kamui and if he does he can just come back. Or better yet kakashi should just stay there, if Obito follows him to the kamui dimension he'll get rofl stomped by kakashi. And if he stays, Sasuke can force him to go intangible, whereby kakashi can land a fatal blow from the other dimension.
Seriously though, Amaterasu spam is key to take down the Bijuu. Kakashi can also rip a couple heads off too. Obito will more than likely not attack since its chakra taxing controlling the Bijuu.
Kakashi can hold off Rinnegan Obito, he won't get caught by kamui and if he does he can just come back. Or better yet kakashi should just stay there, if Obito follows him to the kamui dimension he'll get rofl stomped by kakashi. And if he stays, Sasuke can force him to go intangible, whereby kakashi can land a fatal blow from the other dimension.