The Uchiha and The Senju have descended from an Uzumaki with Rinnegan+Juubi's chakra.
After becoming the Juubi's jinchuuriki with the help of his sealing powers and weapons, he obtained the Rinnegan.
Using the Rinnegan's powers, the SO6P separated the Juubi's chakra from its vessel, sealing the latter away with his Über Juubi chakra powered Chibaku Tensei, which became the moon.
He made the Juubi's chakra entirely his own, and while also having the Rinnegan, the Sage went on to have 2 sons.
The younger was born with the Sage's life force and powerful body resulting from having the Juubi's chakra.
The older was born with the Sage's eyes and powerful chakra.
Hope this makes sense...