Karin, Sayuki and Aina on top. Akari, Tomoko, and Yuka on bottom.
Sayuki is 15 (she'll be 16 in April) and she's been around since late 09. She's a good singer, but I don't have any really good examples to show you because all we have are recordings. She's done some plays and stuff and she was in the Reborn musical with Morning Musume.
Akari is 14 and she joined last spring. She isn't in any of the footage that I know of, but she apparently auditioned for 10th gen, and then again later to be a trainee. Don't know much about her voice.
Tomoko is 17, and she literally JUST joined back in December. She was a finalist in some unrelated audition and I guess they offered her a chance to join the Kenshuushei.
Yuka is 18, was a finalist in the S/mileage auditions, and then did some other UFP audition. She's also in
Green Fields. She's got one line at 3:25.
I'll see if I can find some recordings that might give you an idea of what they sound like. Karin, Sayuki and Aina (who I thought was the best singer in the 9th gen audition) are obviously the vocals and the other three seem more like backup to me.