It is kind of hand-wavy, but sort of like Dom said, maybe Yoda did know Leia would be okay, but he was more concerned with Luke making the wise choice, basically as a way to test him. If Luke couldn’t make the right choice, then maybe he shouldn’t become a Jedi (and Leia should instead once she escapes). Maybe Obi-Wan, knowing who Leia is, couldn’t sense what would happen to her like Yoda could, so he did feel like Luke was their last shot.

Still, the way Yoda says it definitely makes it seem like he is referring to someone Obi-Wan doesn’t know. While “the other” didn’t make sense to me at first, I get why you are suggesting it now.