Multiple mobile robots are a practical platform for realizing the concept of distributed manipulation. New approach for manipulating large number of objects using distributive actuators or agent has been suggested. Multiple mobile robots provide the ability to conduct actions simultaneously from various locations and directions. Using two mobile robots and flexible tool such as a piece of string or rope, a large number of objects that are placed at sparse locations can be sorted and grouped by single action. The Voronoi separation algorithm is proposed as a path generation method for preplanning cooperative actions of multiple robots. The sorting task is conducted on-line using fuzzy logic controller with preplanned subgoals. The proposed control framework was verified by an experiment using two autonomous mobile robots with a flexible tool attachment of fixed length.