1. How did the inheritance take place after the demise of your grand father? Is the property in question the self acquired property of your grand father?
2. If your grand father made a will and bequeathed his entire property in favour of his wife then she became the absolute owner thereof after his demise. If, however, your grand father did not make a will then the property devolved equally on all his legal heirs after his demise, in which event your grand mother's share was equal to the share of your grand father's other legal heirs i.e his children. If your grand mother got a share according to the natural succession then she could have made a will in respect of her own share in the property, whereas if the entire property was bequeathed to her by her husband then she could have made a will in respect of the entire property.
3. If your grand mother passed away without writing a will then the property would devolve on all her legal heirs in equal shares. After the life time of your father you will inherit your father's share in the property of his mother.
4. Your father would succeed to the entire property if he does not have a sibling. The share of your father would devolve on his children including children from his second marriage.
5. Go to the office of the local registrar and ascertain if a will has been executed by your deceased grand mother.