Claim in Deceased Fathers Investment in a flat by PIO

Can A PIO having US green card/ citizenship stake claim in his deceased fathers Investment/advance in a flat which is already in the name of his cousin sister.?by the virtue of a loan availed by cousin sister & serviced by her for the past 5 years

Father expired with out a will.

That is problem,,the will deed or or any other document would be necessary,.Otherwise his heirs can claim share.

To prove the facts in the court need strong evidance to thwart such claim...tey to convince the cousin in america to give u a release deed.

I presume that by PIO you mean a Person of Indian Origin.  A son is class-1 heir to the estate of his father irrespective of wherever he is and whatever his status as to citizenship or PIO etc. If the cousin or anyone else had advanced any loan or credit to the father, such loan or credit has to be first settled.