I think Vader taunting Luke by threatening to turn Leia evil can work even if they aren’t siblings. Luke still cares for her greatly as a close friend and ally, so that would surely tick him off.

And about Leia having the Force, I guess it depends how we decide one has the Force. It technically exists in all beings, and we see through the prequels that the amount of receptivity or natural attunement one has with it is brought through midichlorians. Of course, if an individual has enough, they become a Jedi. I think it’s entirely possible Leia could have some natural receptivity to the Force even if she weren’t a Skywalker.

Now I don’t necessarily want to start a whole debate here over midichlorians, force sensitivity, Lucas, the prequels, etc. So I won’t go too much further with this, I just think it can go both ways is what I’m saying.

But to preserve the way Lucas wrapped up the saga and the way expanded material has built upon it, its easier to just remove the kisses, yes.