User blog comment:Zathronas/Analysis by an Author: Over-analyzing/@comment-173.58.97.227-20131222181845

Good point. Look, I love a good analysis on a subject about as much as anyone else. But I prefer that you disassemble the thing, find out what is established, then leave it at that. We know Yang and Ruby are sisters, be happy with that.

Of course, the easiest way to avoid overanalyzing is to just go and ask the developers for the actual thing that happened. If Monty himself says it, then as the developer what he says goes. Although I'd doubt he'd say it if he wants to say a Grimm fathered Ruby and Yang, then it'd be established a Grimm fathered them.