The Vorkosigan Companion - Lillian Stewart Carl [218]
Vortaine and Vordrozda were heirs to Miles's and Ivan's fathers similarly, and figured in Ezar's calculations as potential successors to Yuri. It is their ages, as closer contemporaries to Aral, that make it more likely that they are grandsons of daughters of Dorca rather than of other daughters of Xav. Confirming this, all the rest of Xav's descendants were eliminated by Yuri's Massacre. The most distant Vortaine can be is third cousin, because if he were a fourth cousin, Gregor would be Ivan's heir before him. In the diagram above, Vortaine and Vordrozda are second cousins to Miles's and Ivan's fathers, thus second cousins once removed to Miles and Ivan. Note that Gregor is also a second cousin once removed.
Padma Vorpatril had no siblings that survived Yuri's Massacre. This also means that Ivan has no first cousins younger than himself on his father's side. Indeed, he seems not to have any first cousins at all, but that may only reflect his mother's attitude about her own family. That Alys Vorpatril chose to maintain very close ties to the Vorkosigans, incidentally thus to the Regent of Barrayar, rather than to other relatives, probably says more about her political interests than about the existence of first cousins to Ivan on his mother's side. However, any first cousins Ivan might have, related to his mother's line, would not be his heirs relative to any titles he might inherit through Prince Xav.
Just the information that Aral "heads the list" eliminates the possibility of any male children of Yuri or any brothers of Yuri and Xav, at least any surviving ones or ones with surviving male children. Aral and Padma, sons of Xav's first and second daughters, respectively, are also mentioned as the only descendants of Xav to survive Yuri's massacre.
We never find out much about Vidal Vordarian's claim. We only know that he spent a lot of time contemplating his genealogy. This implies that there was some problem about his claim, too, but he managed to convince himself of its justice. In order to convince himself that his claim was comparable to Aral Vor kosigan's, his claim needed to differ from Aral's by more than just which of Xav's siblings it derived from. Vordarian may have been the sort of stolid conservative type who could have been convinced simply by the fact that his own line contained no tainted off-worlders. However, Vordarian cannot trace to a brother of Yuri and Xav since none and no heirs of any survived Yuri's Massacre. Possibly he could trace back to a sister, as Vortaine and Vordrozda do. However, let's give him more credit than that, and look at another option.
Say Dorca's sister married a Vordarian from which the descent went straight to Vidal. With Aral appointed as Regent and Vidal Vordarian fearing that Aral would seize the Imperium, Vordarian can argue that his claim is just as good as Aral's (ignoring that Aral has not yet claimed the Imperium) and make his own preemptive strike. The subtle point of which relationship takes precedence, besides depending on precisely what the Barrayaran rules are, is also exactly the sort of thing that often gets decided by strength of arms and spinelessly rubber-stamped by legitimizing bodies afterward.
Without going back to Dorca's great-uncle and what siblings he might have had, just going back to Dorca himself and looking at Dorca's siblings opens up a new set of possible claimants to the Imperium. Actually, these would hardly be new; Yuri must have thought of them, too, and killed as many of them as he could. However, it is also known that he did not get all of them.
If Dorca had a brother whose daughter married a Vordarian, the effect would be essentially the same. We know that there is a female link somewhere just because Vidal is a Vordarian rather than a Vorbarra. So we can easily generate a relationship that