Whats the role of these transistors
I don't just want to answer your homework problem for you, but I'll give you some things to think about.

For Q13,Q1, consider how the collector currents react to a common mode voltage change on Vinp and Vinn, and a differential mode voltage change.  If both Vinp and Vinn were let's say 5V above Vee (and Vcc well above that), then they were both raised by 1 V, what happens to the collector currents of Q13 and Q1?  Now what if Vinp were raised by 1/2 V and Vinn lowered by 1/2 V.  What happens to the collector currents then?

As for Q2 and Q3, look at how they work with Q11.  This is easier to see with one of Q2 or Q3 removed.  Look up something called a "current mirror" after you've thought about it for a while.