You should take the following course of action.
1) Approach the Debt Recovery Tribunal for stay on the auction proceedings initiated by the Bank. Or you may approach the High Court by filing a writ seeking stay of auction proceedings.
This must be your priority since the bank will not stop the auction until you get an order from a competent court.
2) File a criminal complaint before a magistrate u/s 420, 467, 468, 471 IPC or register an FIR directly at the local police station against the person who forged your father's signatures. The investigation in the matter will take some time and after conclusion of the same the charge sheet will be filed before the competent court. After that the trial will start. Hence you must stop the bank first from auctioning the property, so that you may not loose possession. Otherwise third party rights will be crested and it will become very difficult to get hold of the property again.
Contact a local lawyer immediately to proceed in the matter.