Who's more likely to have their rightful property returned expeditiously, the Jew or the gentile?
Statistical likelihood relating to ethnicity of heirs is by the by - the legal basis under which the family lost the property is everything. The individual's religion is not relevant.
The answer anywhere on earth is "a citizen" (presumably without a criminal record).
No and no. Citizenship isn't relevant to ownership (though in Poland there are possibly illegal restrictions on regaining property) and a criminal record or lack of one does not impact on ownership.