What/Why is this poll?
Pick 1 or 2 characters to have significant screentime, wordcount, scenes and "scenes" :^) in the 2nd Arc. Unpicked characters will still have at least have a "scene" or two. So, there's no worry that they'll be completely missed out on.
Khan needs a character to balance out his intensity, but at the same time, having character bloat will only slow updates, complicate the storylines and prove to be an all-around bad writing decision. Having one girl is good, two girls is interesting, but all three is beyond my ability as a writer to deliver.
The Choices:
Second Wave 'Nessa'... was a originally intended to be a throwaway, expy character (Pokemon Sword & Shield). A dead one. But reception to what should have been only a passing mention was surprisingly positive and I have been convinced to keep her alive (though mostly in the background).
If chosen, she can be easily written back into the story in full, due to her fate having been ambiguous. Surprisingly high story potential too, what with her in-story history so far. Katara's not going to like seeing her by Khan's side. Lol.
Ty Lee/Ty Sisters... were the originally intended 'replacements' for the Kyoshi warriors to keep the cast fresh. Also, because she is a fan favourite. Having six of her acrobatic, flexible sisters around has a lot of 'potential.' I have my own take on Ty Lee's and her sisters' characters.
Choosing her with Nessa is going to be interesting to say the least. An old and favourite fan theory is that the Ty sisters have a bit of Air Nomad blood in them; add that with Nessa's pure Water Tribe... and that's almost three Elements in one team. Of course, this also means a good balance of personalities as well.
Suki & Kyoshi Warriors... can be brought back. The final mini-scene edited to end with their rescue if you'd prefer their style of interactions. They still have room to grow as characters, might even give one of them a name too. Lol. But even if left unpicked, they're not done with this story. So, you'll see them again, one way or another.
Choosing the Kyoshi Warriors with anyone else would end as you'd expect it would: Being given the title of 'Honorary Kyoshi Warrior' with everything that implies.