Query pertaining to the Rights over Property in Step Mothers Name.

My Grand Father (Hindu) expired many years back. He was in defense. He has one Son from first wife who expired when the son was too young. He married another women to look after this child. Unfortunately like any Step Mother she didn't take care of that child at all. They gave birth to 5 more kids. My Grand father had purchased property. Some of the property is sold by the step children & money was distributed within themselves only. No share was given to the 1st son. Since the 1st Son was left all alone to struggle he couldn't manage to take it up legally due to lack of finance & support. There is some more property which his father had purchased & the step children are enjoying the benefits of the same. On asking for the share he is told that it is in name of the mother & she is not willing to give it to him so he should forget about his share.We would like to know how good chance do we stand to fight for our rights over my Grand Fathers property.