In this paper, we propose a new haptic interface for two-handed manipulation. The system, named the SPIDAR-G&G system, consists of a pair of string-based 6DOF haptic devices called SPIDAR-G for both hands. By grasping the grip of each SPIDAR-G in each of the user's hands, the user can manipulate one virtual object with their right hand and the other one with their left hand cooperatively, while the user senses interaction force. We evaluated the system by measuring the completion time of a 3D pointing task, and demonstrated enhanced interactivity with virtual objects.