Assuming TBLNGG's concept is elite, high-class and expensive, with a focus on members' individuality (because Teddy), the members we know the most about are genuinely perfect.
Annie Moon (position: probably leader):
First, getting an actual chaebol into the group is inspired. Not only will Annie generate tons of publicity just by existing, she would be a perfect fit for the concept, granting instant credibility, and luxury brands would fall over themselves to get a top idol/chaebol endorsement. Annie would probably be great for the leader position as well since she's an adult (shocking), a graduate of Columbia University, and has been around people in top leadership positions all her life. Don't know her skills yet, but I'm sure they are at least decent if Teddy chose her and her family isn't resisting (they wouldn't want Annie to embarrass the family), and decent is great by current popular group standards.
Bailey Sok (position: main dancer/choreographer):
Getting Bailey Sok into the group is insane. Evidence for her as a TBL trainee has been around for a couple years, but most didn't believe it was possible that Bailey would want to become an idol. She's just too talented, successful and famous within the professional dancer community. It goes without saying that Bailey would would immediately become one of the best dancers (and in-group choreographers) in kpop history, male or female. Bailey has also been training her vocals with one of BTS's vocal coaches over the last couple years. She has a history of getting brand deals, including Nike, and a ton of charisma, on and off stage. Also an adult.
Ella Gross (position: maknae):
Despite her age, Ella has a long history in entertainment/modelling. She has been an internationally recognized model since she was a young child, with a long list of high-end brands that she has promoted. She has also acted in a number of movies/shows. She has the cute factor that would appeal to younger fans while still fitting the luxury concept due to her background (a hard needle to thread). Skill-wise, she has been training at TBL for over five years, while working and going to school, and from what I have heard she sounded good a couple of years ago, so Ella could only be better now.
Chloe Lee (position: ?):
Chloe is likely a member, but little is known about her at this point, other than that she's tall and beautiful in a way that fits with luxury high fashion, and she has a history of modelling.
That leaves main vocalist and main rapper open, but if Teddy could get Bailey as his main dancer then it is likely that he found very talented members for those positions as well.
Also, notice that they are all fluent in English. Assuming the main vocalist and main rapper are talented, the group will have the skills, concept and communication ability to instantly go world-wide (the West generally cares if a singing group can sing, including idols).
Ultimately, the biggest question is whether the music production will match the brilliance of the member selection. If TBL manages to produce quality songs for TBLNGG then the group's dominance is almost guaranteed. If TBL doesn't, the downside of the concept and such a powerful lineup will become clear: it's hard to maintain an elite, high-class and expensive concept when you are flopping.
Update:
Ella is signed to TBL but Bailey isn't officially. For them to make the same move at about the same time can't be a coincidence. I would consider both Ella and Bailey to be almost confirmed members at this point.
Update 2:
Annie Moon and Bailey Sok received GLYF (Somi's highligher brand) and posted it on their insta. This is their only interaction I'm aware of, so I would consider this almost confirmation that Annie (and Bailey) will be in TBLGG.
Earlier evidence for Bailey and Ella:
