Mr. and Mrs. Taggart
Both are dead before the book begins, and we get the sense that neither of them made all that much of an impact on the lives of their children. Mr. Taggart seems aware that his son is a fool and that his daughter has a hard road ahead of her, but he doesn't do anything to help resolve the situation before he dies. Mrs. Taggart, more than anything else, seems hopelessly confused by her daughter. The Taggart parents are only mentioned twice in the whole book, in Chapters 1.3 and 1.5. Dagny's ancestor, Nat Taggart, is a more important influence on her life than her parents.