I think there are some fundamental things about how variables work that you don't understand. However, if you want to do it that way...
Deve:
I get what I am doing wrong, I just do not know how you can have subMenuA, B, C and D listening to Serial.read() at the same time.
That's easy enough.
subMenuA = Serial.read();
subMenuB = subMenuA;
subMenuC = subMenuA;
subMenuD = subMenuA;
Although you could just call it subMenuChar or something and use the same variable in all the submenu functions.