I'm too lazy to do your work. Make not a fragment of the scheme, but the complete scheme. Then to determine the modes in the points of the scheme, use the analysis of the OP. You see the voltage on my circuits. So I did this analysis.

DOn't understand what you mean but okay thanks.. I give up on this circuit : Please how to calculate gain of the other circuit

Thanks

 

.Q3 is to sink current from Q2 and Q4 to source to Q1

As I stated, it does not work to put a current source in the collector, since the collector is also acts as a current source.
You have two current sources fighting each other.

What's the purpose of using a current-source there instead of just a resistor.

And for further help please answer my question about exactly what the circuit is supposed to do.