Complex sentence: The group of painters to which Fattori belonged, who became known as the Macchiaioli, were forerunners of the Impressionists, and like their French counterparts, were criticized for their paintings' lack of conventional finish.
Split into simpler sentences: The group of painters to which Fattori belonged became known as the Macchiaioli. They were forerunners of the Impressionists and, like their French counterparts, were criticized for their paintings' lack of conventional finish.