How to figure out which transistor amplifies the signal?
None on them are "simple resistors". If they were then you'd find a resistor there instead of a transistor.
Every transistor in that circuit is in some way involved in amplifying the signal (although there could be some argument about Q2, since that one is in the feedback loop).
No sane circuit designer is going to use a transistor to do the job of a simple resistor.