To be clear - there is a misprint in the novel.
In the Dramatis Personae, there is a glyph next to Luigi Capecelatro, indicating that he is a character from Shakespeare. This is not true. He is not from Shakespeare. His brother Antony is. As anyone who reads the novel is bound to deduce on their own.
I caught it, but it slipped in due to a miscommunication between myself and the typesetter (ironically I almost wrote "typosetter" - which is unfair as the novel is very well formatted).
So, again - Mari is young Lord Montague. Antony is young Lord Capulet.
Any guesses as to who Cesco is? Mastino? Let the theories fly!