I am sorry but I still do not understand. Let me describe the whole picture as I see it.
vdrive is suppose a sinusoidal of frequency wo, so the primary of T1 has a voltage vdrive in 1 direction (topside positive) during Π/wo (Half period) and the other direction(bottomside positive) during the other half of the input period. So now this variation on the secondary gets transferred as follows.
During the 1st half of the period M2 is ON therefore assuming ideal switching action the drain and thus the topside of primary winding of T2 is at 0 volt. The mid winding of T2 is at VDD. Also during this half period M1 is OFF therefore its drain is floating, so I don't understand why its potential is 2Vdd, I was thinking it will be just Vdd.
Now in the next half of the cycle M2 is OFF and its drain is floating, and M1 is ON and its drain thus the bottomside of primary of T2 is ground. So now why does the floating drain og M2 have to be at 2Vdd? Shouldn't it be just Vdd?
Sorry for being stuck.