How do i get someone's name removed from title of the car if he is not able to mentally sign for title.

You have to find the person that is making decisions for your friend, and find out if they have a Power of Attorney for him.  Is his daughter helping him with decisions?  Do you know if he is mentally competent?  If he is, try to reach him directly and ask to have the title signed.  If he is not, or if you can't find him, you might be able to get a court order to allow you to sign the documents.  If you are going to try that, you would have to prove that you tried everything you can think of to find him.  send letters to his last known address by certified mail so you can either get the return receipt or get the letter back without it being claimed.  Do searches for him on the internet.  If you have his old cell phone number, call it to try and find him.  You will have to present all of that work to the court, and ask a judge to give you an order allowing your signature to serve for both signatures on the loan.  Good luck.