I doubt the show’s creators ever really gave it this much thought, but:
These “witches” (and warlocks). They are NOT like the people in the Harry Potter books. They’re- they’re like friggin’ GODS!! At a minimum, their powers include:
-Instaneous travel through space and time.
-Living for centuries or millenia. (They do appear to finally age, but at a rate of maybe 20 - 50 times slower than “mortals”).
-The ability to materialize any object they can mentally envision.
-The ability to totally alter the mind and personality of mortals in any fashion they choose. (one can only imagine what warlocks do with mortal women.)
-Their origin place is a nebulous realm that’s on another dimensional plane.
I seriously propose that they are actually members of the Q Continuum.