It would make sense for them to help us, since they seem to be enemies of the King. But I also wonder - if he's a threat to them, and they could do something about his presence in liminal space, wouldn't they have already done it?

...you're talking about the Lovers, right? [Armin thinks Chizuru might have a better chance than most of the rest of them in getting help from the Trumps. He won't say that, though - he hates to even think it, but Chizuru's optimism and ability to believe the best of the Trumps, despite the evidence against them, could come in handy in dealing with them. So it's better not to try to puncture that optimism, as long as it's not too dangerously naive. And Armin trusts Hijikata to temper that enough.]