Younger brother submiting fake Will by mother for probate civil court

My father bought a house in the name of my mother in 1953 in Patna from his earnings. I had 1 elder brother, 3 elder sisters and 1 younger brother(6 including me). My mother died on 2-10-1978. In 1984 my father executed a registered deed in Calcutta Court gifting 1/2 of the house to 3 of his daughter including me. 1 of the sister had died in 1974, so he mentioned the names of her minor children making his son-in-law their guardian. 1/2 of the house remained in mothers name. My father died on 15-5-1987. The house was and is still being occupied by younger brothers. In 1995 we (3 sisters) paid the property tax in Patna Mn. Corp. and got mutation done on half of house. In 1999 my elder brother died leaving behind wife, 4 children. In 2007 my younger brother filed in civil court for probate of a fake WILL of mother making him the sole owner of her house in 1977. She used to SIGN but in the WILL she has put only LTI in presence of fake witness. Court has called us to file objection.Wht2do?