The script is very good for Luke's part, but her lines are awful. I don't think anyone could have made her lines work.

I always thought that Han's reaction was on the order of... "huh? oh... OH, COOL!"

As far as the incest thing, to me the most uncomfortable part - in retrospect - was the end of ESB where it looks like with Han gone the other two are going to be a couple. He puts his arm around her and she doesn't object. Who KNOWS what happened between then and their return to Tatooine, eh!?