Electrical – problem with differential amplifier output ..not getting expected voltage at output i.e( V2-V1)..what is wrong here

At first, there is a certain asymmetry caused by the base current for Q3. As a result, Vc1 and Vc2 cannot be equal. Of course, Rc must be chosen properly to allow the correct bias point for Q3.

The one-sided differential gain (referred to the base of Q1) of the main amplifier is Ad=+gm*Rc/2. Thus, the transconductance gm - set by the current source I1 - plays a main role.

It is no surprise that any change of Ic and/or Rc influences the bias point for Q3 and the quiescent voltage Vo. This is a classical "offset" effect. But you should not try to feed back a voltage from the Vo node to the base of Q2. This would result in POSITIVE feedback (instability). But a feedback path to the base of Q1 should work. However, the gain of the whole circuit will be affected, of course.

From your updated schematic, it is clear that there is a problem with R9/R19. Either R9 is essentially shorted, or R19 is essentially open. With pin 3 held at 2 volts, the op amp is otherwise working just fine.