Thanks for suggestion, Davioware, but that's not what I was searching for :)
As you said, creating a new istance of a Family, a random object will be created, but you don't know which one.
About the first solution, that is for sure the most straight one, but also the less "pure" one :) As a matter of fact, if you use that method, each time you add a sprite to your project for any reason (e.g. new release with new sprites, or different sprites depending of user, or whatever) you must add a new condition to the "switch case" and this will slow your algorithm, instead of picking the i-th istance of an array...
However, if there is no other solution, I will of course pick that one, thank you :)