Many of the quotes that you speak of are ones that many fans have had the most problems with.
I guess you could tell your friends that every film adaptation has changes, and these are some examples of that (this would be bascially stepping around the problem). Then you could go on to tell an abbreviated version of the true Arwen story, or tell your friends to go out and get the book so they can figure it out for themselves (but then they would still be confused).
Basically the story of Arwen that I have determined and read is that she has no immortality, no choice no more, she's mortal. The quote from the film though I think refers to the time that she will have to go through after Aragorn has died, and when she will be all alone. But they wanted to make it sound more dramatic than something like "she will wander around till she dies" (which is basically what happens to her).
The other is just a troubled quote with no explaination. It's like the whole Faramir being mean thing
