This paper presents a constrained optimization framework that enables the implementation of multi-robot constraints, as virtual fixtures, to assist human operators, in a teleoperated scenario. The collaborative constraints guide the motion of multiple robots such that the spatial and temporal relationships are maintained between them, while following human input motion objectives. We demonstrate this control architecture for the task of manipulating a surgical knot to a target point. The teleoperation system uses four arms from a da Vinci Surgical System® (two master manipulators and two slave manipulators), with custom electronics and software. It extends previous work, which focused on a cooperatively controlled system where the motions of two robots were directly controlled by user-applied forces. Our current system enables us to effectively evaluate the accuracy of the knot positioning task and completion time in a clinically realistic setup for Minimally Invasive Surgery.