Other than Madara, who among the Uchiha Clan possesses or successfully awaken the Rinnegan? I'm just curious whether if only Madara possesses the Rinnegan and if not how many are there?
What are the chances that Sasuke can awaken his Rinnegan?
I just realized that the correct answer may be potentially wrong.

As we have seen thus far, Madara and Obito are the only 2 Uchiha to have used the Rinnegan. Aside from them, Sasuke is the only other Uchiha clan member that is still alive, whom hasn't awaken the Rinnegan yet.

With that said, Sasuke is potentially capable of awakening the Rinnegan any second now. Sasuke has bitten Karin many times. Karin is an Uzumaki, which is a distant relative of the Senju. That means Sasuke has Senju cells inside of him!

With the DNA requirements fulfilled, Sasuke can pull a quick one and activate Rinnegan stunning Madara, the Shinobi alliance, and all of us readers :)

Updated with known Rinnegan users:
Madara,
Obito,
Sasuke,
Sage of 6 Paths,
Kaguya