The last months of his life, I took total care of him, cleaning up urine, because he couldn't get to the bathroom, washing his clothes, bathing him, all at my home... never once did his family ask if he needed anything or offer a helping hand. He wanted me to have one of the vehicles, my payment from him for taking care of him when he passed away. His family didn't even know how he wanted to be buried, and they took everything, even the truck that was in my possession. Now they have it for sale. His step brother even was given a vehicle. Do I have a legal right to sue the family for the truck for taking care of him, and as he wished? They (his family) never had anything to do with him until it came down to what they wanted from him.... there was no will.
I am so very sorry you have been treated this way. The reasonable thing would have been for your friend to change the truck title to your name while you were caring for him, and to see to it you had other possessions he wanted you to have.
Others may have experience to guess about the likelihood of you winning. I just offer my condolences.