Note, that this code can create 2 or 3 instances of the same sprite. If you need to create 3 different sprites, it's a bit more difficult.
This is made a lot easier with the Advanced Random plugin, which allows you to create permutation tables.
I've included three ways of doing it in this demo:
1) Spawn a random family member - this has the benefit that you can use non-numbered sprite names, but can result in repeats.
2) Use a permutation table to pick a numbered sprite - no repeats.
3) Use a permutation table and an array loaded with the family member names to pick a non-numbered sprite - no repeats.