Is it a sin to add Ali, Murtaza, Hasan, Hossain, etc. at the end of the name?
All of the above names carry beautiful meanings. So there is nothing wrong with keeping it. However, according to the Aqeedah of the Shi'ah, it would be shirk to keep them in the hope of cure and special virtues. Shi'ara says, "I have five people through whom I can cure all incurable diseases." They are Mustafa, Murtaza, his two sons (Hasan-Hussein) and Fatima.