They're also missing the weird yellow and black robot character whose name I forgot. He was on the team around the same time as all of the rest although I don't recall if he was an original member or not. Wasn't there also a kind of lame character whose ability was being able to speak all different languages after hearing them or something else not very useful for fighting bad guys?
That would be Warlock, who showed up later (after Magik, IIRC). And Doug Ramsey/Cypher I mentioned in my post. Also, he was not lame, he was pretty damn cool, especially after he realized that he could understand a bit of how Warlock worked since his abilities included computer language, and the two teamed up.
Just for reference, the original team, as per the original graphic novel, was Rahne Sinclair (Wolfsbane), Sam Guthrie (Cannonball), Danielle Moonstar (Psyche, later Mirage), Xi'an Coy Manh (Karma), and Roberto da Costa (Sunspot). Amara Aquilla (Magma) first appeared in New Mutants #8. Doug Ramsey (Cypher) first appeared in New Mutants #13, and Illyana Rasputina (Magik) first appeared (as Magik, previously she was a child) in New Mutants #14, but neither joined the team immediately after their first appearance. Illyana did join before Doug, as Doug joined alongside Warlock, who first appeared in New mutants #18.
Assuming they're going anything by the comics, Storm was the mentor of the team after she lost her powers. At that time, Xi'an had rejoined the team (she left before Amara joined), and the team was comprised of Sam, Dani, Rahne, Xi'an, Roberto, Illyana, Amara, Doug, and Warlock. Now, Xi'an was... obese... at the time, but they don't have to use
that part of the storyline (she regains her original form soon after, although
that won't be used, either, since it involves Loki). I do agree that Warlock would be hard to animate, and Doug, while being cool, doesn't have powers that would translate well on screen. Still, other than the confirmed Sam, Dani, Rahne, Roberto, and Illyana, we do still need Xi'an and Amara. The only reason I can see them leaving those two off would be because the team would be too female-heavy. In which case they could easily use either other characters (who may or may not have joined the New Mutants formally at any point, I personally wouldn't be averse to seeing Jonothan Starsmore (Chamber) or Everett Thomas (Synch) from Gen X included), or make up a couple new ones. You'd have a good ethnic mix, too. American, Native American (Cherokee, specifically), Scottish, Brazilian, Russian, Vietnamese, and European (Amara's country doesn't actually exist in the real world). Plus, Xi'an being lesbian, leaving her out, with her being a founding member of the team, has some unfortunate implications, other than her being the only Asian on the team.