Since your father had died without leaving any WILL, his property will go in equal share amongst his Class-I heirs viz., his widow (i.e. your mother), his children and also his mother (in case she is alive).
First, one has to obtain legal heir certificate from the Tehasildar by submitting a detailed application indicating all the Class-I heirs left behind by the deceased, their age, their relationship with the deceased (i.e. wife, son, daughter, mother etc.). The said Application should be accompanied by the Death Certificate.
After making enquiries, the Tehasildar will issue the legal heir certificate.
On the basis of the said legal heir certificate, the legal heirs have to approach the Authorities for mutation of the property in their name.
However, you want that the property should be registered in your mother's name. For this, all the other legal heirs have to execute a Registered Relinquishment Deed relinquishing their respective shares in the property in favour of your mother. The Relinquishment Deed will involve very small stamp duty and registration fee.
Once such a Relinquishment Deed is registered, then your mother can approach the authorities along with the legal heir certificate and the Relinquishment Deed for getting the property mutated in her name.