dmv website is your friend:
California Title Transfers - DMV Titling & Registration Information Online - DMV Guide
once you get the title, find out if it has "and" between the names, or if it has "or". should be one or the other. if it has both, then i think you can consider it "or" for purposes of requiring signatures to make your change to the title.
if the title has "and" in between the two owner names, then both owners must sign the paperwork to make the change. (e.g., both owners must agree to the sale of the car).
if the title has "or" in between the two owner names, then either owner can sign the paperwork to make the change (e.g., either owner can sell the car without consent of the other named owner).
hope that helps