Is writing the Adhan 100 times daily and playing it in the home considered part of the Sunnah, and how can my relative be disabused of his belief that he is bewitched due to being influenced by interpreters of dreams and dispellers of magic?

There is no harm for Ruqah (exorcists) in recommending what they have experienced to have a positive effect in treating one afflicted by magic, as long as it does not involve Shirk (associating partners with Allah). There is also no harm in performing Shar'i Ruqyah (Islamically permissible incantation) for both the afflicted and the non-afflicted. To overcome this ordeal, it is recommended to consult psychiatrists, consistently perform protective dhikr (remembrance of Allah) and ta'awwudhat (seeking refuge with Allah), integrate into society, keep company with the righteous, and avoid following channels that caused this to him.