If Hindu males and females die without a will, the property belonging to them is governed under Hindu Succession Act, 1956. Whatever property was held by the male is distributed among Class I heirs, Class II heirs, agnates, and cognates in the same priority order. Section 10 of the Act gives the list of Class I heirs which include:
Widow of a predeceased son,
Son of a predeceased son, and so on.
After the 2005 amendment in the Act, the daughters were also added as the legal heirs and they had equal rights on the property as any other Class I heir. Therefore, in your case, the property of the father will be equally divided among his children as they are the legal heirs and they need to apply for an heirship certificate from the court.
In the case of a Hindu female dying intestate, the property first goes to her husband and children, and if they are not alive, then to the legal heirs of the husband. But in your case, your mother's property will also be distributed equally among the three children and for this also you will have to apply for an heirship certificate at the court.