I think i'd have rather seen beast than Emma. Not becauase I don't like Emma but because after glancing at the way beast has been acting on krakoa, thoughts about sublime beast and that one line of black swan...
"You are you Henry Phillip MCCoy? Other you's have tried this before. The Beast is not a name unknown in the game of worlds"
It should have been beast and not only that since Xavier gave him the MIND STONE to hold in his death. . . I think beast should be using krakoa and all those events to set himself up as the puppet master of mutantkind. He's everything
Sinister wanted to be plus some or could be, but the idea that he's a scientist and IN TUNE with what the Illuminati would believe in originally make him the best choice.
Adam doesn't belong here... at all.. Not because of power but because he's ... He's unsullied in a way that marvel could use to make him an equal version of theier superman. Him just being good or doing the right thing on that "Cap giving a speech" level of righteousness fits him more than this. Everything about the CHARACTER of the blue marve i.e. his character and nobility inform me that he'd be a PROBLEM for the illuminati not someone to join them.
"What do we do about adam..." or "How do we keep Blue Marvel off the board during this" is a thing they could do that would show they consider all factors and also *nod* that he's a powerful character under no ones control. (Lone shooters are always a problem).
TLDR: Sorry if this sounds like gibberish hope I got it across. Imho Beast is a better fit than emma (and hell he could make himself telepathic) and Adam Brashear might have moved in secret but NOT to gain control. He's oppose this and he's not beholden to any of them so he'd be a noticeable interference point they're aware of as well. "Hmph. If we do this what about Doom..."; "and" Hard Stares "What about Professor Brashear..." my thoughts