Did Cleopatra have a baby with her brother?

No, never. For one, Cleopatra hated her brothers and they hated her. Their marriage, was strictly for political reasons, as Cleo and her elder brother were made heirs by their father and were co-rulers. For two, she was 22 years old at the time of her first marriage and her brother was twelve. Her second brother, which she married, was only ten years old. Babies were out of the question.