For Gaara's case I find that even if Gaara is freed from his seal he would not be of much use, for me the ideal would be that he sacrifices himself by taking one of the shinjus with him to the other world.

The only solution to save Naruto and Hinata would be to convince Kawaki, which is going to be super hard given his mentality and determination.

So the most realistic would be Sasuke since it is enough just to defeat Hidari again. (which has already been done)

It's either Gaara or Sasuke for sure, if Naruto or Hinata gets released, it'll only be because Boruto fought Kawaki and forced him to release them, which isn't gonna happen anytime soon. I don't think Gaara's gonna get killed anytime soon though.

100% sasuke

Naruto and Hinata likely aren’t gonna be releases until the end of the series, maybe before the likely fight with shibai at the earliest

Gaara would be too weak to help, and I wouldn’t be surprised if he got eaten just to show what happens when a Shinju gets their target

Sasuke is the only one Boruto is actively trying to free rn, and he’s the one who could help the most

Killing Gaara off would be crazy though, who's gonna replace him as Kazekage, Kankuro?

Or temari ?