Complex sentence: Ludovico married Ercole I d'Este's youngest daughter Beatrice d'Este in January 1491 in a double Sforza-Este marriage, while Beatrice's brother, Alfonso d'Este, married Anna Sforza, the sister of Gian Galeazzo Sforza.
Split into simpler sentences: Ludovico married Ercole I d'Este's youngest daughter Beatrice d'Este in January 1491 in a double Sforza-Este marriage. Ludovico Sforza married Beatrice d'Este, while Beatrice's brother, Alfonso d'Este, married Anna Sforza, the sister of Gian Galeazzo Sforza.