Purpose of these two transistors
They act like a diode to bias the output transistor bases. They are like a Vbe multiplier (also known as a rubber diode - see here)  without the multiplication (i.e R1 0&Omega;, R2 infinite in the diagram below), so the drop is ~0.6V.
In a class AB or class B amp they are often used to provide a trimmable ~2*Vbe drop to bias the output transistors:



Note the input is at the upper side, so one ~2*Vbe multiplier (~1.4V, depending on desired bias)) can be used. In your circuit it's in the middle, so you need 2 drops each of around 0.6V.