Juubi and Rikudou's brother?
I don't think there are two Juubis, because in the final clash between Ten-Tails and Kaguya's sons, Hagoromo and Hamura, they managed to defeat the beast and sealed it within Hagoromo. However, knowing that his death would unleash the Ten-Tails back into the world where it would continue its rampage and reclaim the chakra that humanity now possesses, Hagoromo separated the monster's chakra from its body and used his Creation of All Things ability to create the nine ,tailed beasts. Hagoromo then used Chibaku Tensei to seal the Ten-Tails' husk, i.e the moon.