Complex sentence: His father, Anton Gretzky, has been described as having "been born in Russia with Ukrainian forebears", while "the only Slavic language spoken in the Gretzky family (was) Ukrainian".
Split into simpler sentences: His father, Anton Gretzky, has also been described as having "been born in Russia with Ukrainian forebears". In addition, "the only Slavic language spoken in the Gretzky family (was) Ukrainian".