A flexible dual-master-dual-slave teleoperation system is proposed. On the master side, a new control law with a variable dominance factor is proposed to offer the system high flexibility and ease of training. A new wave-based Time Domain Passivity Approach (TDPA) is deployed to guarantee the channel passivity and high transparency in the presence of random time delays. The proposed algorithm is validated by applying it to a multilateral teleoperation platform consisting of four 3-DOF haptic devices configured as two masters and two slaves. The results demonstrate the feasibility of the proposed system in different complex tasks and its superior performance compared to previous work.