Please guide for heriship certificate

Legal terms are being confused in your case .
Procedure are also confused in your case. 

Provision of State Co-operatative society law , rules regualtion are also not followed , means lengthy procedure are adopted I feel some time. 
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1) Who purchased the flat on whose name , Take for Eg your father "XYZ"

2) XYZ who are his successor , widow , son , daughter , etc. mother (imp) , give relationship no individual name

3)  Whether he made any will . Registered /Unregistered

4) Who reside in flat (Not imp. just for curosity)

5) Nomination done or not done
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Now out of multiple way to go to destination best and easiest way has to be chosen and not lengthy and costliest . Thats logic