Aha! If samoht04's male got a female, then it must be random. They're not related, right? Save/reload to the rescue!
Edit: Reporting back, got her a male on the first try. I'm pretty surprised that they have the prejudice response to each other. Unfortunately he's an Excitable boy, so between his "Woohoo!"s and his "A simbot!"s, their romantic interactions keep getting reset to the beginning. While they have woohoo'd successfully, the going steady, engaged, or married options haven't been offered.