Complex sentence: Just prior to Marvin's death in 1970, the firm was sold to an employee, William R. Surman and since his death in 1993, it was being run by his son Robert Surman.
Split into simpler sentences: Just prior to Marvin Probst's death in 1970, the firm was sold to an employee, William R. Surman. After his death in 1993, the practice was run by his son Robert Surman.