Query related ancestral property

Hi Sir, Please help with below issues. My father have two wives. As his first wife is not used to stay with him for long time he got married to my mother in year 1984. He have 2 children from first marriage. That time he got arrested for second marriage when first wife complaint against him & to settle the issue my grandfather made gift deed of ancestral property land on name of my step brother in year 1987. That time my three uncles are above 18 year old but there approval not taken to made gift deed of ancestral property. Due to some reason possession is not taken by them also his name not registered on 7/12 in 1987. And uncles was unaware about gift deed. In year 2007 my grandfather was passed away. After long time in year 2014 my step brother claimed that property. And by paying bribe he got register his name on 7/12. Talathi taken his name on 7/12 without giving any notice to my father or my uncles. 1) Can we challenge that gift deed? Also my father is received property from his parents, some is transferred from fathers name & some from mothers name. Now my step brother is clamming his share in fathers property too. 2) Can my father exclude my step brother from partition of his property. 3) As my mother is second wife of my father, is she can get the share in his property. Thanks in advance.