Is an affidavit before a first class magistrate enough for succession

My late uncle had his property in two districts of WB -- Howrah & Purba Bardhaman. He was a bachelor and died making a hand-written will in my favor. This is yet to probate. When he died, he had my father and three sisters alive. Later one sister died after 1 year. Certainly the dead sister's son & daughter have sent us an affidavit made before a first class judicial magistrate of alipore (24 parganas) court stating him intestate and showing my father, other two sisters and them as uncle's successor. My question is -- 1. If such an affidavit is valid in case of succession? 2. what I shall have to do now. They are pressuring my father to forget the hand-written will and sale the house.