There was a period in history when Montclair was part of a fallen kingdom that extended north and west. It went down to the coast and into the country beyond the mountains that bordered the ducal family's estate.
However, territorial disputes led to Castille assuming control of Montclair. As expected of an old kingdom with bloodthirsty rulers, their borders changed significantly through time.
It surprised many when the marquess' family was never stripped of titles. However, their willingness to bring their wine business to Castille and benefit the greater population healed their reputation and doubts about their loyalty to a new monarch were pushed into the history books.
That was why the titles of marquess and marchioness weren't stripped from the Martin family despite no longer being against a foreign border. They were the gateway into the capital and it felt like enough reason to keep the same title considering its history.