Answer
Moulay Ismail's main opponent within his family was Moulay Ahmed ben Mehrez, who claimed the title of sultan in 1672. Ahmed ben Mehrez was the son of Moulay Ismail's brother, Moulay Abdellah, who had been sultan before Moulay Ismail. Ahmed ben Mehrez was a powerful figure in the Moroccan court, and he was able to rally support for his claim to the throne.