Who are the foil characters in My Brilliant Friend?

Foil characters come in pairs, and their function is to highlight different character traits in one another. For example, in The Simpsons, Bart and Lisa are foil characters because Bart's naughtiness emphasizes by contrast Lisa's good behavior. Likewise, Homer and Marge are foil characters because Marge's sensible, responsible personality is emphasized by being always contrasted by Homer's unthinking, irresponsible behavior.
In My Brilliant Friend, the main characters, Elena and Lila, are foil characters in a number of different ways. Lila, for example, is usually brave and daring, which emphasizes how sensible and cautious Elena usually is. Lila is also precocious and instinctively smart, whereas Elena is more mild-mannered and conscientiously studious.
Antonio Cappuccio and Nino Sarratore are also foil characters. Elena is attracted to both. Her attraction to Antonio is a very physical attraction, whereas her attraction to Nino is more about an intellectual connection. Simplified, Antonio and Nino represent the age-old brawn versus brains dichotomy. They are foil characters because each exists as a character in part to emphasize the opposite trait of the other.