Would Raudra and Puragon even be capable of negotiating with Mark and the rest? Not just because they're, you know, completely insane, but they haven't exactly had the most human contact, what with them living out their entire immortal existances in caramped caves inside a cliff, so they probably haven't had a lot of chances to brush up on their English. Would they have any idea of what Mark is talking about?
Who ever said they've lived out their entire immortal existences in cramped caves inside a cliff? If they were another
set of dragons that can't even communicate properly because they've been locked up their entire lives and also hate each other, that would be some mighty facepalm-worthy lack of differentiation between them and the Dragons of Ouen. (I mean, it's bad enough as it is, with just the shared elemental-dragons-who-hate-each-other theme.)
In fact, it's been made pretty explicit that they haven't been living out their immortal existences in those caves. First they matured in different places around the world, then Dragoreen rallied them all against Preciure, then a feud broke out between them, then they squabbled over who should get their mother's cave, then they did whatever but were sighted (so clearly they got out sometimes), then they came out to fight Mark and company rather than Mark and company sneaking up on them, then they went and talked to Mew and Mewtwo. If nothing else, the fact they managed to complain to Mew and Mewtwo makes it pretty clear that yes, they can talk. (Not English, obviously, but that's never been a problem for any Pokémon in this fic.)
They would be perfectly capable of understanding what Mark is talking about, but seeing as yes, they are kind of batshit, they won't necessarily respond to it in any way sane people would consider rational.