aunt died and no will

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My aunt died 3 weeks ago and her legal guardian was the Jewish Association for Services for the Aged. Myself and my family haven't seen her for 20 years, prior to seeing her at the hospital a month ago. She had a co-op apartment and no will. She was never married and has no children. My dad is her closest living relative, but he is 89 years old. So I need to take over this matter, but I don't know where to start? Please help me.