The first sign in this episode says Chef, Eric Cartman, Stan Marsh, Kyle Broflovski, Kenny McCormick, and Dr. Alphonse Mephisto are thirty-five miles from the Hell's Pass Hospital.
No one reall knows who Eric Cartman's mom is because Eric Cartman didn't want to know.
However, Cartman and Kyle share the same blood type. So there is a possibility that Cartman's Mom is actually Kyle's mom as well. Which would make them half brothers to one another.