Repo! The Genetic Opera Question

[indiana_j]

So, in Repo! it's pretty obvious that Luigi Largo is, what, late 30's, early 40's?  Or at least that's what he looks like.  Pavi's a bit harder to place because, you know, he looks pretty youthful but he is kind of wearing someone else's face; but he came across as the middle sibling and certainly older than Amber - early to mid 30's, perhaps?  But then you have Amber, who seems to be around the same age of Shilo - 16 to, perhaps, early 20's, if that.

Obviously, by the time Marni showed up in the picture for Rotti, he was no longer married to Luigi and Pavi's mother for some reason; I'm wondering if Amber's probably a half-sister, then, considering the age differences and the fact that Rotti was looking to remarry?