Is raising both index fingers after ablution, upon reciting the Tashahhud, from the Sunnah, or only the index finger of the right hand? And what is the ruling on that?

There is no evidence for the Sunnah (definition) of raising one or both index fingers when reciting the prescribed remembrance after ablution. However, it is legislated to raise the hands and gaze and to supplicate with the reported supplications, such as: "I bear witness that there is no god but Allah, and that Muhammad is His servant and Messenger," or "O Allah, make me among those who repent and among those who purify themselves." The Shafi'is and Hanbalis have explicitly stated the Sunnah of facing the Qiblah and raising the hands and gaze towards the sky when reciting the remembrance after ablution.