"•What if Natalie and Richard's parents had lived?"

Maybe they did. I mean, I know it's generally accepted fanon that they're dead; but I don't think it's actually said. Or am I misremembering dialogue?

(As a matter of minor interest, when I was working on the never-finished fifth season, i.e. FK5, I wrote an episode in which their parents came to visit Natalie and lamented having been out of the country on holiday when Richard died.)