How shall I reverse the polarity of the signal for C? Any simple approach?

When you say 'reverse the polarity' do you mean pulse 'B' is High going from 0V to +V and 'C' is Low going from +V to 0V..?

 

When you say 'reverse the polarity' do you mean pulse 'B' is High going from 0V to +V and 'C' is Low going from +V to 0V..?

"B" goes 0 to +5 volts
"C" goes 0 to -5 volts

 

The monostable multivibrator chips provide both Q and Q-inverted outputs.

For 0 to -5V you will need a bipolar power supply and a level shifter circuit.

 

I have ended up with this design. The output in this simulation is quite acceptable.
Pot A and Pot B are ganged together. The right op-amp is powered with dual supply and the remaining two with single supply.

Shall appreciate your valued comments/suggestions for refinement/improvement.