In law, the legal heirs of your father are entitled to continue the oil mill of your father and
1) You should apply to register of firms to transfer the proprietary firm to your mother by submitting the documents mentioned below
2) All stocks can be sold by the legal heirs of your father.
3) You should apply to respective authorities for transfer of boiler license , pollution license etc to your mother's name by submitting the documents mentioned below.
4) You can also get the insurance on factory transferred from your father's name to your mother's name.
5) Required documents are
a) Your father's death certificate.
b) Family member certificate of your father (wherein the names of legal heirs of your father is provided by Mandal revenue officer)
c) Name transfer applications for proprietorship, boiler licenses, pollution , GST , and other applicable licenses.
6) You can also approach the district court and apply for succession certificate for all the properties of your father including the oil mill and if all the legal heirs agree to transfer the property to your mother, court will direct transfer of all licenses pertaining to your mother . In districts, issue of succession certificate will not take more than 6 months.
Hope this information is useful.