I note that at least anecdotally, this has not been an uncommon experience among highly-qualified legacy applicants to these sorts of colleges in my circles (meaning lots of deferrals, then some get accepted RD, some not). I actually wonder sometimes if being a legacy in ED is a bit of a double-edged sword in that they may reason that even if they defer you, if they do accept you RD you may still be very likely to yield, more maybe than a non-legacy would.
In any event, I am noting this because I think the OP needs to be prepared for this scenario. Specifically, suppose you are deferred by Duke–do you then actually apply ED2 to Vandy? If you are actually admitted by Vandy, that means you can’t go to Duke even if you would have been admitted RD.
Again, just from experience, I can say a lot if kids in those circumstances decided not to ED2. And again, some got into their deferral school, but most did not, and they attended a school that admitted them in RD.
Which wasn’t necessarily a bad outcome at all. In fact my own S24 was in this situation, and he ended up admitted RD to the school that would have been his ED2, and that is where he ended up since his deferral school ultimately rejected him.
Still, this just emphasizes why it is very helpful to have a robust list of Likelies and Targets that you would be excited to attend. Because among many other things, it can make you more confident in not doing ED2 if your ED1/REA/SCEA college defers you.