What role is this Matched PNP Transistor and MOSFET pair playing in this circuit?
peufeu is right in his comment, this behaves as an “ideal” diode.

If the voltage in TP21 is higher than the voltage in TP20, then Q1-2 will be blocked and Q1-1 will behave like a diode. R6 will pull Q2’s gate to ground and the current will flow through Q2.

If the voltage in TP20 is higher than the voltage in TP21, then Q1-1 will be blocked and Q1-2 will be saturated, pulling Q2’s gate to 5V, preventing the current from flowing through Q2.