As noted, it's possible that when in humanoid/human-like bodies ("nordic types") they do not have telepathic abilities. Or, maybe they do, but that's still a problem because it's always possible that the human "elite" have someone at the meeting with telepathic abilities, who could in theory listen in on the "aliens" private telepathic communications. The point being, IF the human elite have people with telepathic abilities at these meetings, then the aliens using telepathic communication to discuss nefarious plans with each other is obviously a bad idea. Using spoken language to communicate would seem to be the most secure option, as long as they use a language they know that the humans cannot understand, hence their use of the Atlantean lang. that is an ancestor of Basque. Hence also, the humans attempt to get an AI (i.e. no consciousness) translator to find out what they are saying without the aliens knowing that they are doing it.
I don't think we've really thought enough about the idea of telepathy. The 'hot take' on it is that you can "read everyone's mind" or something, but I'd say it is nowhere near that simple or easy. I think most people tend to think about telepathy from the perspective of being the only person with that ability in a world of non telepathic people. At least, that's how it's most often portrayed in movies (which sadly are a strong reference point for many people). If you're telepathic, but everyone knows you're telepathic, and they are too, then your telepathy isn't really that special. It would essentially be as "special" as being able to speak a language in 3D, where everyone else can too.