This is clearly impossible, as cheryls dad harry died in a car accident, and you actually see where heathers dad dies. Total alternate universe. similar to that of another game i've played over and over (Kingdom hearts) theres two of each person. one in the real world and one in an alternate world each have different names etc. so in this instance the real world would be heather and the other world would be cheryl.
Well at least thats the way i see it.
No, it's just not canon.
As for Kingdom Hearts...oh boy. There are no alternate universes in it either and there are not 2 of each person. Nobodies of certain people are created when one loses their heart, and their names are anagrames with an X added in somewhere due to reasons I can't explain without spoilers. Are you positive you've played the game over and over?
But to make it clear, neither game has an alternate universe/worlds. (I love both series. heh.)