Perhaps your question is whether the relative speed of approach of the two particles is 2c, is this so? Yes, it is 2c and this does not violate the principles of relativity, because such speed is not the speed of a particle, but it is just a derived value. On the other hand, the speed of a photon is c regardless of the inertial frame.
Contrary to other answers, the velocity from the velocity addition formulaand is notcalculated by the relative velocityspeed formula, it is the velocity measuredgiven in a different inertial frame. Relative velocity is simply the difference of velocities measured in a specific inertial frameprevious answers.