Again my answer doesn't quite fit any of the listed choices. I liked the Rylands as one rival family. I also like they idea behind the McCay Brothers, Carter's grandsons, as rivals to John Ross and Christopher (and "Rebecca" would have made more sense as McCay's granddaughter). IRC in some of your fan fiction stories you've introduced a son of Marilee Stone as a rival, I think something like that is also a good potential idea, in terms of having enemies that are connected to the original series and are part of the Dallas legacy. But the Barnes feud was over, and Jeremy Wendell never any children (because he was obviously gay), so I wouldn't try to force new rivalries there.