No family member that can pass away
Nothing happens. 

The rules do not directly give an answer to this outright; but they are clear that a family member that is not visible; or has not been born yet; cannot die. So you simply cannot kill any village member. The game asks you to do something impossible; so you don’t do it. It is a common rule in other board games in general that you “only do as much as possible”. 

There are a couple threads on BGG that agree with this interpretation. 

https://boardgamegeek.com/thread/1323745/passing-away-nobody-visible

https://boardgamegeek.com/thread/761561/about-family-member-pass-away