That is literally not fucking true. They could each hold their own keys, one could, two could. There are a lot more than one single way for keys to be managed. And I think it's retarded to delegate key management for an entire family to a single person. At least a single key. A multisig setup would be better, but still far from  the ONLY way.

Think a little. It won't kill you. 

 Oh yes 

 Woulda shoulda coulda. Reality is different and one is enough. Do your parents hold keys? Grandparents? Children? 
Yea. I thought so...