The reason very basic words like Father are shared between Iranian and Spanish is because they both ultimately descend from an ancient Indo-European language likely spoken in present day Kazakhstan around 5000 years ago. Steppe pastoralists that spoke this language colonized Europe in the Bronze age. Their language evolved into the various Celtic, Latin, Slavic and Germanic languages of Europe. Greek also comes from this ancient language. Compare Latin, Greek, Avestan and Sanskrit and you will get chills at how similar they are.