What should we make of Egg’s sisters, Rhae and Daella, who appear to have married and had children? Why everybody insists so much on Robert’s Targ blood but ignore about these other lines with Targ blood? Did those lines died out? Were killed during Robert’s Rebellion? Their Targ connection is close enough to make it relevant.

To be honest, we don’t know very much about Rhae and Daella: who they married, what happened to their children, etc. Certainly, they don’t show up at all in discussions of the reigns of Aegon V, Jaehaerys II, or Aerys II, which doesn’t exactly cream out that those lines were extant and politically relevant in the later Targaryen dynasty. 

But as to Robert’s Targaryen blood, he would be the more proximate claimant than any descendants of those lines, since he descended from a daughter of the more recent King Aegon V rather than a daughter of Maekar I.