Application for a legal guardian of a minor.

my seniors brother and his wife met with an accident and passed away leaving a minor child. My senior is unmarried and so he wants his mother, i.e, grandmother of the minor child to be appointed as a legal guardian to the minor. can someone please tell me how should he apply for a application for guardianship before DC. what are all the documents that are required to give the advocate he appoints. what is process of applying for it in the DC of Hyderabad. please someone guide. anticipating for a response.