Disclaimer: I do not own these guys.
Arwen
Strengths: Making rivers obey her command; she has a great dad and brothers
Weaknesses: Likes Aragorn
Disorder (mental): Thinks she saw the vision of the future in which she is married to Aragorn and they have a child
Favourite Food: Artichoke Hearts
Probable Cure: Going to Valinor
Warning: We know of no other cure for the patient's mental condition. We suggest letting her do whatever she wants, since if you don't problems will result. She will definitely resist going to Valinor unless Aragorn can go with her. Therefore the best thing to do is leave her in Gondor. We are not responsible etc.
Haldir
Strengths: Dying epic-ly; nice red cape
Weaknesses: Dies
Disorder (mental): Thinks he is proud to fight alongside men once more
Favourite Food: Spinach Strawberry salad
Probable Cure: Fighting alongside men once more and dying
Warning: As the cure involves death, of course it is not recommended. As the patient's malady is not dangerous or very harmful to him, we suggest letting him just live with it.
Lindir*
Strength: Is good at being a servant and counselor
Weakness: Looks like a girl
Disorder (mental): Nanosophobia**
Favourite Food: Carrots
Probable Cure: Having to have Dwarves in Rivendell for an extended amount of time
Warning: We are not responsible for any destruction or havoc caused by the cure. Rivendell may never look the same again. Also, the cure will be extremely uncomfortable for the patient.
*Lindir is not very well-known to those who have only seen the LOTR films. He is the dark-haired Elf in Rivendell. In The Hobbit, he is more noticeable, being the one who tells Lord Elrond that the Dwarves have left Rivendell.
**This is the fear of Dwarves. It is not a medically recognized name for the fear, but as there is no other word for it (at least in our library of psychological terms) we have had to use it here.