If it was clearly incest though there’s still the question of why they had Big Mac and Marble interact the way they did. Marblemac shippers could at least have the argument that they were far enough in relation that it’s still legal. Or perhaps the Apples and Pies weren’t family… yet (Referring to how if Big Mac and Marble got married then they really would be family). You have to remember the episode where AJ and Pinkie tried to discover their family roots to see if they’re family it left it vague/open to interpretation pretty much.

Not that it matters that much anymore after this episode. But yeah. 

And I know a new writer wrote the episode as well. Just seemed like they were told mainly about Hearts and Hooves Day but was never told about the Season 5 episode with Pinkie’s family celebrating Hearth’s Warming with AJ’s family.