[Discussion] Does anyone else think that Kaguya was under some kind of possession?

[MAN OF SIN]

It doesn't matter if they knew about Kaguya or not. They were all originally the Ten Tails.

They were just made out of its chakra. This doesn't mean they they know everything about it.

 

[Zawerni]

They were just made out of its chakra. This doesn't mean they they know everything about it.

They still know more than anyone else, with the exception of Kaguya herself. Her merging with the Shinju created the monster form of the Ten Tails. It's reasonable that the Ten Tails could transform back into its Shinju form, which it did as noted by Gyuki.