You will have to get a Succession Certificate which will show all the heirs of your father . All heirs except your mother will have to waive all rights to the property in favor of your mother. With these documents the Registrar of your Zone will affect transfer of the property in your mother's name.
Succession Certificate is supposed to be issued at nominal cost. Normally the local District Magistrate / Tehsildar of the Zone your father resided last is the person to be contacted. You should visit that office to know more details / costs etc. There are drafters / notaries generally sitting outside the SDM's office ( at least they are in Delhi ) who could advise you further. The Registrar's Office where the property is situated could also guide you on the same.
DISCLAIMER : General information and advice provided is without any warranties as to suitability for any use, correctness and application to any specific case. Please always take proper legal counsel . However, if it helped anyone even a little a " thanks" via the " Thank Contributor " button would be appreciated and would encourage me to keep on making efforts :-) . I am also always open to corrections and further learnings from more experienced Seniors here.For DIRECT contact with me / my friends and more law related informations / queries visit https://getjoy.in/r/q