The Thenardiers were very vague in the musical. They did not include Azelma or the two younger sons of Monsier and Madame Thenardier. It was also unclear if Gavroche was even part of the family or not. I think this is because 'Zelma really did not have an important in the book anyway. Same with her two younger brothers. If some of you disagree with me, i'm sorry, but this is based only on my opinion. And Gavroche, well I don't think the audience needs to know if he was actually a Thenardier or not. But in the book, it said that Gavroche was part of the Jondrette family and the Jondrette family is actually the Thenardiers. They only showed Eponine, Thenardier and Madame Thenardier because they had significant roles. Thank you!