I used to work for AARP Auto Insurance, and i will tell you directly what i was taught....
If there are three names on the registration, that would most likely mean that the car was registered under the estate of. If one person has passed away, and there is a mutal agreement between you and the other person...then you can take both of your statements to where you have your car registered and fill out some paperwork for them to change it into whomevers name. But first you're going to need to find out on the registration about the person who passed away, if they had any hiers to the car. Because if the car was meant to become in the name of anyone else, you would need thier consent to change the registration as well.
Also, make sure you have this lined out and peachy keen with your insurance as well, often times ins companies will not insure those vehicles, or else if they do, and the registration information on the vehicle is incorrect, they may not pay anything if anything should ever happen to that car.
Another thing you can do, because every state is crazy and has different laws concerning that, you should call your dmv or ins company and have them look up the state specifics, and what is required for a vehicle registered in the "estate of"
Good Luck.