Unless those 5 kids are born at the same exact moment, the environment will likely evolve one way or another, as well as the financial situation of the parents. Quite often, older brothers/sisters are more "motivated" than the younger one because the parents are still trying to get it together early on, so they see and are part of that struggle, while having to help out too. Younger kids help out less, and (this is my case) parents are "better off" when they are being raised, so they don't see that much struggle and end up a lil more complacent/less motivated. That's not even taking into account the friends of the respective children and the influence they will have on each of those 5. Only valid comparison is between twins who for some reason would grow up in different environments.
Genetics basically sounds too "deterministic" to me, I have a hard time believing that all is played at birth