Is the voltage from peak to peak my thevenin in voltage?
Whether a voltage is the Thevenin equivalent or something else doesn't change the qualifier that it is peak to peak, just peak, RMS, or something else.  For example, consider this circuit:



The Thevenin equivalent at OUT is 2.67 V with 667 &Omega; impedance.  If the 8 V of the V1 is RMS, then the 2.67 V at OUT is RMS.  If it was 8 Vpp, then the value at OUT is 2.67 Vpp.  The fact that a Thevenin equivalence was computed doesn't change how the voltage is qualified.

You could just as well consider p-p, p, and RMS to be different units of EMF.  One could be in volts, one in frimmels, and the other in blorks.  If the source V1 has EMF of 8 blorks, then the OUT will have EMF of 2.67 blorks with 667 &Omega; impedance.