What is the legal status of a heir enjoying sole possession on mother’s intestate property since 7 years?

The 3 heirs are in dispute. According to verbal family agreement, One heir took his share and left property 12 years back. Second one left it 7 years back after taking his share. Third one is staying alone with his family in this property. Both of them now are not willing to sign on property papers to give third his full rights and are demanding equal share in this property. What should he do to get his right in property.