Is what is happening—hearing a voice asking me to wear a ring on my right hand to protect it from demonic possession, and the jinn confirming that the jinn causing the possession has been imprisoned by a righteous saint who died 400 years ago because of the ring—a reality, and what should I do?

What your family mentions about the wali’s influence, and your friend’s belief in awliya (saints), are superstitions with no basis in reality. Benefit and harm are in the hand of Allah alone. It is not permissible for you to wear a ring with the intention of protection from jinn, as it is among the forbidden amulets. As for your family’s belief in the deceased shaykh, it is clear misguidance, and you must explain to them that benefit and harm are in the hand of Allah alone. What you heard as a sound in your ear might be an illusion or from the jinn, and you must seek treatment only through legitimate Islamic methods.