Layering in the War Within

Hey im new to wow and have begun tailoring and enchanting - to pursue my proffesions i am hunting cloth drops and gear to disenchant, but when i got to the world boss in hallowfall that is suposedly good for those drops, it is ALWAYS occupied for hours and even days at a time, ive found that if im lucky enough i can find a custom group for cloth farm, and it will phase out the people in the area that are their so that now it is just me and my new team. alot of the time i will be kicked for under performing but one time i wasnt. After about half an hour of farming this event with my team we seemed to swap layers again, the original team that was occupying the area came back and we were forced to disband as we could not compete with them for the farm.
so basically after that explanation my questions are as follows :

  1. How do you change the “layer” you play on so that you can get an area to yourself?
  2. What causes me to keep changing between layers ruining the experience?