Hi Ashwini,
I think what you are trying to get is two isolated supplies off a single transformer?
It is technically possible by using a transformer with two separate, isolated secondary windings. Then separate voltage regulator circuits such as LM317 (variable) or LM7805 and LM7812, which would give isolation of both the positive and negative side of each output.
You would need to have something like a 0 – 12 + 0 – 12 transformer with a full bridge rectifier on each winding.
It’s an odd configration but one which used to turn up on old televisions to keep the HT circuits isolated from the rest. Basically we didn’t want to be touching anything remotely connected to 25KV,.. because it hurt!!