You are not supposed to barely turn on the transistors by applying only 0.68V to their base. You are supposed to apply a big voltage to the 1k series base resistor so that the transistor has enough base current to turn on completely. If +5V is applied to the 1k series base resistor then the base current is (5V-0.7V)/1k= 4.3mA and the transistor is turned on completely.
The Mosfets are too small for more than only 2.7A, which is only 5.4V across the 2 ohms load resistor. If you actually build the circuit then the tiny Mosfets would fry.