I can't really speak on much like this til I've seen the whole of the show, but my own early thoughts were to use Greg and Laura's daughter Meg who the MacKenzies raised as a hotshot political operative caught between two worlds and moral compasses, as well as maybe either Diana or Michael's (or Olivia's) gay son named for Eric, and maybe Daniel Avery. How you would weave any of them organically back into that locale is hard to make plausible, obviously.
I thought about the twins but tbh my idea for Bobby Jr. was tied mainly to an idea of a brief, one-season revival and conclusion to Dallas, where eco-crusader Bobby II (or Betsy!) would go back to Texas and clash with one of J.R.'s sons over the future of the business and the climate crisis at large. Like Gary, he would be kind of the fairhaired boy with a pristine vision of the future. But that's for another thread. (The better idea, inverting the 'good/bad' Ewing boys and making Christopher the baddie as David Jacobs suggested, is obvious, but I was operating as though Dallas 2012 is canon and therefore Christopher is dead, so you had to use other heirs of J.R. while I would have John Ross in a more conflicted and soulful role.)