Multiple siblings, twins, etc., at one SA or across a few, happens more often then you would think. It's fun to watch.
There are 4 sisters, 3 USNA grads, 1 graduating USNA this year, see link. All were near the top of their USNA class, and all earned immediate post-grad opportunities, Harvard, Fulbright, Cambridge, etc. The three commissioned ones are excelling. (Non-USNA sister went rogue to Duke and is successful in her civilian career.)
http://centuryair.com/news/the-five-asdal-sisters-all-pilots-and-graduates-of-century-air/
We have a USNA sponsor alumni daughter whose younger sisters are at USNA and USMA, same year. That will make for an interesting dual Comm Week freeway dash.