moroccan limo company owner is believed to have shot four members of his family before taking his own life , police said .
he then is believed to have gone upstairs to shoot dead his sister-in-law , 26-year-old meriem ben yahia , and their mother , 76-year-old kenza benzakour , on the ground floor of their phoenix , arizona on thursday .
police said it appears the man and his relatives were in an on-going dispute over the family business .