Though Mr. Ferrars is already deceased when the novel opens, we know that he was the husband of Mrs. Ferrars and the father of Edward and Robert Ferrars and Mrs. Fanny Dashwood.
We are told that he died “very rich” and managed to leave almost the whole of his fortune to his eldest son Edward in such a way that it depended on “the will of his mother.” As Edward was educated privately but younger brother Robert went to public school, it’s entirely possible that Mr. Ferrars’ status and/or wealth increased over the course of the boys’ childhoods. As he was able to write his widow's input so wholly into his son's inheritance, it seems likely that the fortune was gathered during his lifetime and is not an ancestral estate.