Interesting, given that the original Runaways stuff did have a lot with the X-Men often on. Given that Scarlet Witch and Quicksilver lost their mutant status, it has seemed like Marvel would happy de-mutate any mutants not part of the X-Men franchise for marketing reasons.
Read that story once, but I thought they were foster siblings, at best. It would explain that weird comment about their "pure" marriage, though, in the original series.
Sure, Molly's parents could be non-mutants and Molly herself could be, but it was pretty important in the original series that the Hayes were factually mutants; the original story falls apart otherwise.