How is it that two brothers are both named Luke? (i.e., Luke and Little Luke) Is this a West Virginia kind of thing?

Also, was it ever revealed or even discussed in any show how and when Luke, Hassie, and Little Luke were orphaned?

I don't remember ever hearing how Luke, Hassie and Little Luke lost their parents. But being from WV I do know that naming siblings the same name is not a 'WV thing'.
In one episode Granpa explains that "when Little Luke was born, his parents were so excited about having a boy, they named him Luke, forgetting that they had another son Luke". Thus we got Little Luke...