Joe Johnson is Jeremy and Suzy Johnson's uncle and brother of Jack Johnson. He owns a restaurant in downtown Danville: Uncle Joe's Subs. The business even has its own van, shaped like a submarine sandwich to serve as a mobile advertisement.
He appears to be very kind to Candace as well as his nephew and niece, going so far as to put Candace's picture on the menu and name the grilled cheese 'The Candace Special' after his nephew asked him about it. ("Journey to the Center of Candace", "One Good Scare Ought to Do It!")
Joe's last name has not been stated in an episode, but based on appearance, he may be from Jeremy's father's side of the family with the last name of Johnson. He is the owner of "Uncle Joe's Subs".