Is there a way to correctly set TCP to the end of the robotiq 2-pinger gripper?
Yes, there is a way to do this. Robotiq might actually support this in their URCap automatically. I would ask this in the https://dof.robotiq.com/, because it is particular to the that Robotiq have designed their products.
The TCP and center of mass are listed in the instruction manual at section 5.2.3