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aww so it's because they were kidnappedI wouldn't call those "an Awakening," though. Yes, "Awakening" is the name given to the pillars, it's the name of the room in KH1. But the OP seems to be talking about the experience. The process of "awakening" to their powers. The character customization sequence, in other words, but that's maybe a little restrictive.
If you're going to count every character who's ever been at the stained glass platforms, then Riku already has, because he was there at the end of DDD. Data-Roxas too, though that wasn't a "real" Awakening.
If you're only going to count people who have been to their own hearts... well, okay, I see where you're coming from, but I'm just not feeling it.
As to Kairi, Alice and Jasmine, that I can talk about. Kairi, Alice and Jasmine aren't visible on the platforms in Sora's Awakening because they haven't been kidnapped yet. This is mostly so they're still a surprise to the player, but we can come up with an in-story reason if we want. I always assumed it was because they aren't yet aware of their role as Princesses of Heart. Maleficent likes to talk, the other Princesses must know why they've been kidnapped by now.